There's a related, annoying situation with Ping and buying multiple items - as a buyer, you can't change your shipping option when paying with Ping. so if the seller offers combined shipping at a reduced rate, you can't pay with Ping, because you obviously don't know whether you'll win 1 or more auctions until after they're over, so you don't know whether to pick the full rate or the discounted rate for each item. Ping's only usable for single-item purchases, which is very frustrating. Allowing the seller to change the amount charged via Ping post-sale would fix this. Then they could combin...