Should we assume miracle believers usually tell the truth when they see miracles?

Richard Swinburne put forward the Principle of Testimony. It says it is rational and correct to hold that people usually tell the truth. (See page 84, Philosophy of Religion for A Level, OCR Edition Anne Jordan, Neil Lockyer and Edwin Tate, Nelson Thornes Ltd, 1999). He points out that though people will think this approach is dangerous we all accept it unless there are solid reasons for assuming a person is not telling the truth. He spoke of the Principle of Credulity - it says I should accept your perception of what you have experienced unless there is evidence that you are lying, unless you are not acting like the experience really happened, unless you have been taking mind altering drugs, unless you are inconsistent (your story keeps changing and contradicting itself) or unless you have a better explanation for what the person experienced for their perception is not necessarily correct. Swinburne held that if a lot of people report perceptions of God, all together they point to the possible existence of God. They make a cumulative case.

But we cannot say that something major such as God sending plagues to kill children in Egypt or a man rising from the dead or a man curing one sick person while sicker ones are uncured is true for people say so and people usually tell the truth. Usually is not good enough for such serious stuff. It is not even respectful to God or faith or evidence.
And if mind altering drugs annul what you say what if there are mind altering supernatural powers as well? What if the miracles of Jesus never happened but certain people were afflicted with a mind altering supernatural illness that made them think it happened?

It sounds reasonable to say that miracles must be believed to happen for it is natural for us to believe people when they testify to anything possible such as miracles. If we are going to dismiss what they say then we must ask why we would believe anybody when they testify to anything. We know by experience that most testimonies to anything are wrong or deceitful or mistaken. We find this out day by day in ordinary conversation. Many of the things we believe on somebody’s testimony are false and we just don’t know it yet and probably never will. The sceptical version of a miracle story is one exception among several versions that say the miracle was real. In other words, testimonies and evidences that the miracle is false are harder to get than ones that it is true. That problem is universally common. This proves that the testimony argument is worthless when it comes to miracles. Nobody is interested in finding out that the Amityville Horror was a hoax. Despite its conclusive refutation, the story is still popular and still appearing everywhere as the truth.

Swinburne might use a cumulative case but hardly any believer does or can do it. That is why overall, if testimony to miracles is fine as grounds to believe in practice this does not happen and miracles are just trouble.