If I'd spent $700 on a used iMac and found out that it was in unusable condition - I'd have protested to the seller and if that failed to eBay.
Did and did. The $700 loss was AFTER I got money back from eBay/PayPal. That brings up another lesson. If there's something wrong, don't be nice and reasonable and try and work with the seller. And, if for some reason you do, don't have any money the seller gives you for repairs go through PayPal.
I worked with the seller for several weeks - lugging the 27" iMac back and forth to the store. He was reasonable at first and payed me back for the repairs. However, at the end, he wouldn't pay or even return my messages - or even eBay's messages. And, because the money he had sent me was through PayPay and referenced the original eBay purchase, eBay marked that money as a seller refund which was deducted from my purchase price when they ruled in my favor. Therefore, I ended up eating all the repair costs - and returning the iMac to the seller - and paying for that shipping!
I was an idiot since most Macs on eBay only go for a little more than the cost of a refurb on Apple's site - which includes a year warranty! I try not to think about it