Yea I have to agree with Solax on this one, there really isn't much to do with this currently as a rule. The only way to make it safer through the game itself would be to code a new feature into the safe trade system that allows you to put your paypal money on there as a pending transaction waiting for confirmation to send instead of just TC or items. Wether or not the developers would want to do that is another question. The only problem I see with doing it like that though is that Toribash would probably add on a transaction fee to using your paypal through safe trade, which is fair since you're using their security to prevents scams, though the added transaction fee might scare people away from using it.

Two more possibilities I that just came to mind. Toribash is a steam game, would there be any way to make it where you could offer funds from your steam wallet through safe trade?
If you don't want to do that then try this nest idea instead. Update the items you own in toribash to appear as items in your steam inventory, then transactions
through the steam trading system could also become possible for a safe way to trade your stuff. Though this isn't really paypal like you were originally talking about.