Evidence comes in bits.  Some evidences are conclusive.  Others are not.  A conclusive argument arises when it is all looked at together.  We will learn that nothing in favour of a miracle is ever conclusive.  No argument as a whole that a particular miracle is real works either.

Reason is the method for weeding out stupidity and contradictions.
You can have reasons to believe in something and your belief can still be unreasonable. A belief can be reasonable and you can believe in it for unreasonable reasons.
That is a problem with all belief. But if your belief is too far-fetched and magical, you demand suspicion that you are depending on unreasonable reasons.
If you claim you are reasonable you have to prove it. You have no right to just claim it. Remember proving that you are reasonable is not the same thing as proving your belief. A reasonable person shows he uses the right method and that is more important than what the method results in. He does not cheat people by asking them to believe he is reasonable.
You need to be skilled at reason and give exceptionally good reasons to believe the exceptionally hard to believe.

Ordinary and non-ordinary
Miracles are improbable in the extreme. That is not calling them impossible. A miracle is a supernatural event. It is a wonder. Miracles have to be considered to be very improbable. Christians agree that they must be very improbable otherwise they wouldn’t be miracles. They wouldn’t be signs of God’s love and an invitation from him to join his true faith and the religion he founded in order to save us from man-made religion. It follows then we must have extremely good evidence to believe in them.
An extraordinary claim is one that is out of the ordinary. A miracle is totally out of the ordinary. Very odd things can happen naturally but a miracle is in a totally different league. Thus if you need strong evidence that a five year old boy is the best computer hacker of all time you need even stronger verification if he claims to be a god or something.

Verify that you cannot verify
You can verify that you cannot verify a supernatural claim.
If the supernatural/paranormal takes place and leaves you verifying that you cannot verify it then that is something supernatural/paranormal telling you that it does not care about evidence. Should you assume that the supernatural/paranormal always cares? Yes would mean arguing that if you cannot verify that the supernatural/paranormal is involved that means it is not! No would mean the supernatural/paranormal is random and thus a miracle can be taken as just an oddity not as anything that is intended by God to be meaningful for us.
If the supernatural happens and you verify that you cannot verify it then clearly as the supernatural does not like evidence, then if you want to have a chance to verify it you need as much solid and careful evidence as you do for the assertion that Hitler drank water.
What level and standard of evidence?
The evidence required for something very unusual at the bare minimum must be independent evidence.  There is not a single independent witness of the resurrection of Jesus.

What happens when you hear of a supernatural event? You may think it is a natural event mistaken for a magical or supernatural event. You may think lies are being told. You may say you need solid evidence before you believe so you are keeping an open mind. You might believe.

If I say I have built a tree house, you wouldn’t need much evidence for that. It’s not unusual so you could take my testimony as sufficient evidence. But if I said I built a spaceship that could go to the moon you would need to see and test the spaceship before you could believe me. A miracle would be even more extraordinary. Its more out of the ordinary. Having the spaceship would be strange but at least it would be a natural event.
A miracle being supernatural would be stranger and even more unusual. If miracles are routine events and happen too much, the message they allegedly convey from God will not be taken very seriously. We need to test and check out the evidence very carefully. Then we can work out if miracles are believable.

Magical claims (a miracle is a magical claim) would need exceptionally good and exceptionally comprehensive evidence - no gaps. The believers say the unbelievers in miracles are making the bar so high that no evidence would be any good. That is nonsense - all we want is the evidence to cover all holes and gaps and to be exceptionally good. For example, we need a CCTV recording of Jesus rising from the dead. They say we will make out its interfered with. But unless we have evidence we cannot assume that. And they cannot assume that we would be that corrupt either.  We take it at face value. If we ignore the CCTV without reason the fault is in us. It does not prove that exceptionally good evidence can be done without. Our faults are irrelevant.
We would need to investigate to see what alleged miracle has the best evidence. This would set the bar for us. It would tell us that we need better evidence than that before we consider ourselves justified in believing in a miracle.
Not all cases of something being shown true beyond all reasonable doubt are equally strong. We need evidence for a miracle that is as good as the evidence say for a murder conviction which is strongly beyond reasonable doubt. That religion has a problem with us needing that speaks volumes.
Evidence for one miracle cannot annul evidence for a contrary one
What if there is evidence for Jesus’ miracles and it is better than the evidence say for the miracles of some other character such as Apollonius? It would mean that you consider the miracles of Jesus to be the best supported. But it would not mean that you can dismiss the other ones as well. They would have to be afforded inferior belief. There is no grounds for dismissing them and that is just bias and dishonesty.
Christians need ordinary good evidence for their supernatural claims if they want to ignore or dismiss contrary claims. They need good evidence that the other claims are false.
To afford strong faith to Jesus' miracles and lesser to others leads to gullibility which is another reason why really good evidence is required.

Our damaged faculties
Religion says that our reasoning powers are damaged because Adam and Eve turned away from God and damaged us and put sin in us. They are right that our faculties have problems though wrong to blame original sin for it. Science shows that our cognitive and intellectual faculties never function to their full potential and often the potential is not high enough. Even if our reason is diminished that does not mean we cannot expect good evidence before we believe in religion. In fact it means the evidence should be exceptionally good and remarkably good. You would need as good of evidence that Jesus is still alive as you would that your cousin is still alive.
The argument from ignorance

People say that miracles are unlikely so even if they happen we have no reason to believe in them. Religion can have only one response to this: “How do you know what’s likely?” This reply shows how religion refuses to be self-correcting. Science looks for evidence against its discoveries as well as evidence for them. Faith looks for only the evidence for its claims. It is inherently biased and unfair. It leads to aggression that is aroused by fear.
Miracles by definition and in our outlook are not very likely. You don't expect the snow on your path to just vanish despite 6 inches falling on it through the freezing night. So we need evidence that is abnormally good to justify believing in something that is so unlikely as a miracle. If something is very unlikely you need marvellous evidence for it. You would need evidence for example that Mary appeared at Lourdes that is as good as the evidence if not better than that the Queen of England visited Ireland in 2011. Religion answers that we do not know what is unlikely. It does not believe this at all for we cannot be happy and make plans if we believe that! Miracles then attack the beliefs and confidence we need.
Religionists lie about the evidence

Evidence cannot tell you if something is supernatural or might be supernatural. That is not its job. It can show that there is no known source of the blood when a statue of Jesus weeps blood. That is all it can do.

Belief in miracles is about wanting to believe and has no real regard for evidence though believers will manipulatively cover that up.

It is more likely when a miracle or supernatural event or alteration of natural law is reported that the report is false for people lie and make mistakes even if you can’t explain the reports. You may be mystified at the strange puddle on your floor but you know it didn’t just appear there even if two reliable people testify that it did.  If human nature lies so much about testable stuff then non-testable claims such as miracles will attract more lies.

Are sceptics against miracles guilty of bias?

Everybody agrees that a miracle is what is not ordinary. Religious people say they are supernatural acts of God. Atheists do not believe in miracles. If you say that only the ordinary happens you are accused of bias. You will be told that not everything that happens is ordinary. But in fact it is. What is ordinary and what we see as ordinary are not the same thing. We make mistakes about what is ordinary. We think an athlete breaking some world record is not ordinary but if we knew how much training she did and how healthily she eats we would not see it as ordinary at all. What is extraordinary is really only in our heads. Miracle and magic if they happen are the only real extraordinary.

If you demand good enough evidence before you will believe in the supernatural, people will tell you you believe in natural things on less evidence. They insinuate that you are exhibiting a prejudice against claims of miracles or supernatural happenings or religion. They say it is not fair that you make your standard higher when it is a claim that can be categorised as a religious or spiritual or supernatural one. They are also implying that if you demand good enough evidence before you will believe in the supernatural claim, then that is unfair if you believe in other supernatural things on less evidence.
But nature is extraordinary not just the supernatural
The laws of nature are so unlikely and yet we have them. They are extraordinary. The evidence for them is near-undeniable. So we have extraordinary evidence for nature working a certain way. A miracle needs extraordinary evidence not just because it is extraordinary but because nature is extraordinary. To reject miracles as nonsense is about preferring extraordinary nature to the supernatural. It is wiser to prefer to assume that nature is extraordinary instead of looking for extraordinary miracles. Why? If nature is amazing that should be enough for you.

A miracle is never scientific in the sense that every detail is recorded and given to a scientist for examination. When something happens in the past, lots of the details will be lost forever and forgotten forever. Religion still sends in scientists when it wants to consider a miracle claim but that is stupid and pointless. It shows that religion agrees with the sceptics that its allegedly miraculous origin should not be taken seriously but it won't admit it. The science is really about hiding what nonsense it is. It is about lending it a false aura of credence and importance.

Extraordinary claims require extraordinary evidence as in hard evidence at best and that is a science principle. The religious won't even admit that any miracle report or magic report needs to be backed up by a higher standard of evidence that what you would need for anything else. No miracle story gives us such evidence.