If Ebay weren't such complete wankers I'd say it is wrong to deprive them of their fees.

He put wheels on their site having agreed to the fee structure.
Ebay put him in touch with a willing buyer.
He sold his wheels and he got an acceptable price.
Therefore ebay have done their bit and now he doesn't want to pay them.

To me, that is wrong.

But Ebay are even more wrong with a lot of the shit they pull so bollocks to them!!!