The miracles Jesus did had plenty of witnesses and were impossible for the technology of His day or ours. (Well, except the water to wine part. David Copperfield could probably manage that one.)
Could it all be a lie? Sure. Is it probably a lie given what we know about all those eyewitnesses and how heroically they lived, suffered and died? Not likely.
The beautiful thing about God's plan is that it sorts all men into keepers or rejects by their own willingness to round off the uncertainty in God's favor or not.