Reputation won't fix the problem. A buyer with a stolen paypal account only needs to make one purchase to make a profit (he doesn't care about reputation). It usually goes something like this:
1. Buyer with a stolen paypal account sends the payment
2. Seller sees the payment and sends the coins
3. The actual account owner sees the charge and contacts paypal to refund the charge
4. Paypal does a chargeback and takes the payment back from the seller
Now the paypal thief has the coins, while the seller is left with no payment and no coins.
i dont see big problem with scenario you describe here, because there is not so much stolen accounts.
bigger issue is to do chargeback on purpose by the real account owner.
I just want you to understand that chargebacks are going to be a huge problem. Whether it is from stolen paypal accounts or users doing chargebacks on their own account, you still have the same problem (seller loses money). This is the reason no one else accepts paypal for cryptocoins.
