Email the person and explain you thought they were complete phones and ask if you could cancel the deal. That way neither of you would get negative feedback. If it's a no go. Then.

Unless you have paid a lot of money for them. I would resell them one at a time with full description and cut your losses. That way you both retain 100% feed back.

If he's selling them with a misleading description, they are likely no use to him or anyone else as replacement cases.

Either way, I think you'll probably find there is something in his advert that will absolve him, in which case it's Caveat Emptor - although the price should probably have told you that they are just dummies.

Was it a BIN or were you bidding against other similarly mislead punters?

If the price is disproportionate to the worth and you feel the advert was misleading, appeal.

"Hello I have just bought eight "Display phones" off Ebay by mistake, *the seller gave me second chance offer cause what he has done is put the advert as if they are REAL phones and not empty carcasses?"

Does this highlighted bit mean that you bought the phones, out-with eBay?

If you only paid a tenner,put it down to experience. If you were foolish enough to believe that you were being sold 8 mobile phones for £10 then I think you are either very naive or very stupid. I apologise for my bluntness.