Im pretty sure ANY paypal transaction can be charged back, its ridiculous tbh, only thing i can suggest is to only sell to trust worthy people, but that will greatly reduce your audience.
player auctions is very simple, the thing that makes it secure is that.. it is accredited by the BBB. When you buy gold:
You send your payment to PA, they alert the gold seller, the gold seller then gives the gold to the buyer, then PA gives the money the buyer sent to the gold seller... it's a middle man system which is amazing