is dr.faustus crazy or sane?

You need to take Faustus in the context of the period. Faustus is set in the 1580's. Marlow published it in 1604 or 1616. In the 1600's, most stories took on Biblical allusions or themes so in that sense the story is plausible. It is essentially a Judeo-Christian morality tale. Dr. Faustus wants it all. He is an academic with an insatiable thirst for knowledge, wealth and the finer things that the world has to offer. Really that's not far off from what most people want today except for, perhaps, the knowledge. So Faust isn't really so mad. He is willing to sell his soul for what he wants but I wager many people today do the same thing. Perhaps it is not to the Devil but certainly to other things. It takes allot for Faustus to repent his sins but he does in the end. I would say Faustus was quite sane.