Seems to be a fraud deterrent. I once had an eBay listing that was "purchased" by a Nigerian scammer. Buyers need to have a reputation system as well in a viable eBay replacement.
Yup - I think from a technical aspect we could totally have a user purchase before creating an account / signing in, however this limits us when it comes to dealing with fraud as well as brings up problems with the escrow system.
Since all payments enter escrow, without an account, the buyer can't release the payment to the seller.
Since all payments enter escrow, without an account, the buyer can't release the payment to the seller.