Several points...
Ebay is weighted toward the buyers nowadays, and they dont, or will rarely delete unfair feedback unless it contains swearing etc.
The first set of rollers look in, and were advertised as fantastic condition, the photos look good, so you're not really going to be able to say he's brought a duffer, then brought yours to make a good set, blaming you (unfairly) in the end.
Has he left feedback ?
If he hasnt, stonewall him. If he gives a neg, do what you can to get it retracted (although i dont rate your chances)...and accept it happens.
Its ebay....it's likely to happen, so personally i wont lose any sleep, or let it ruin my day.
I've sold 2 items (amongst hundreds of others) to what turned out to be a completely unreasonable buyers. I quite rightly refused to refund etc etc. They threatened negs....but never carried it out.
I always put in the replies something along the lines...'i realise you can give me a negative. I stand by my description, and i'll leave it to your concience'
This hopefully lets them know you're not going to be bullied.
One final point...i have heard of people making chargebacks through Paypal. I gather they can reclaim their money and you dont always even get the item back !!! I'm not sure what, if anything you can do to prevent this. May be worth checking out. TBF, if you've got ebay on side, you should be ok.
Good luck....its a real bitch when this happens.