I'm no expert on tires or wheels but I've spent a lifetime negotiating, and the key is to put yourself in the position where you've given the other side a motivating reason to say yes. In many, if not most, negotiations you can manipulate the situation to where the choice that best fits your needs is the one that motivates the other side.

In this case I'm betting the least attractive thing is for the E-Bay seller to take the items back by paying for the shipping, only to have to sell an item already out of his or her inventory. The most attractive thing is for him or her to give away most or all profit in order for this situation to go away. On the other side your best bet is to come up with a way to keep the wheels you wanted, and find a way to change the tires to a size you can use.

To that end you offer the seller no negative feedback on the premise he or she made an honest mistake (which is almost certainly the case here). This is return for the seller to make you whole on any loss for keeping the rims, and swapping out the tires either by selling or trading them.

1. You have to put out some time and effort for the sale / swap

2. The seller has to put out some money so you're not upside down

3. You both agree to let bygones be bygones and move on

I believe that a good compromise, and if the seller doesn't agree he or she is not a very good business person. My bet is he or she will jump at the offer, and you'll end up with some fabulous rims and NEW tires.