Should I hold them to the price?

a deal is a deal. i have sold a easy 250g worth of goodies on eBay. and i have screwed up like this before and NEVER asked somebody to end the deal because i screwed up. they got their parts for what they paid. the seller did not proofread the ad, to me it would be different if the seller emailed and said he was sorry for the mixup but to lie and say the auction was for gaskets is wrong and i would ask for my valve covers. thats the part that would make me mad. the seller isnt honest.