Basically it boils down to this.
If i am Joe
[email protected] with 50,000 in my account how am i supposed to ascertain if a user who buys something from me is using a "fraud" account..
If i sell
[email protected] a domain for $20 i not only risk losing the $20 , but i also risk losing my 50 grand that you will seize when you find joescammer@epassporte has sent me $20 ( without any way of me verifying this )