Tell him to pay you 300$ up front regarding of the nature of the object. So there is no risk for you.
Also, you can ask for the full payment up front too ..
Can you no longer set your actions to require certain amounts of feedback before someone can place a bid/buy?
ebay only lets you do -1 , -2, -3 feedbacks. you can't auto block ALL zero people. You can cancel bids, then place them on block list. this guy won the item already. it's very easy to solve the situation. CALL PAYPAL. say I want to verify this payment, they will call the person who made it, verify it, and they can no longer do an unauthorized charge. of course can still do item not as described or not recieved.I still see sellers do that but it's in their ad right upfront. You can't change the rules after you've made the sale.
Tell him to pay you 300$ up front regarding of the nature of the object. So there is no risk for you.
Also, you can ask for the full payment up front too ..