You enter into a binding contract for the purchase on an Ebay sale. As far as the buyer is concerned as long as the product is what is pictured and described, you can't really go in and negotiate after the fact. It is pure auctioning, at an in-person auction you have the same responsibility to pay up your price. The only guarantee for the seller (sort-of) is when the item is shipped. Pickup only items leave a big grey area so are risky for the seller. If the seller has indicated they accept Paypal and no other stipulations are posted in the sale, they really have no right for complaint.
Sounds to me like both the buyer and seller in this case do not have a clear understanding of the Ebay auctioning process and rules. Read the rules and understand what both parties rights and responsibilities are before you list a game or enter into a binding purchase contract. If you expect a certain method of payment as a seller, state it clearly in the items auction and if you are a buyer, know what you are getting into before you make the bid or hit the buy it now.