Many of the relations and early youth ties that were forced from Warbeck in his confession turned out to be real and verified people under later inquiry.
All that I have read about Warbeck indicates a fraud brought about by wishful thinking on those that helped him in his claim.
Yes, I have my doubts about Warbeck too. But Henry 7 certainly had other doubts - and after viciously and horribly torturing and murdering him - he destroyed his face. Very uncommon to do that but people thought that handsome Warbeck facially resembled the young prince.