Personally, I wouldn't risk it.
What happens if it has 5 bad pixels on the display? You can't walk it into the eBay reseller, if you complain they will just say "Meh, call Apple" and Apple will say: send it in for warranty and wait. We won't issue a replacement on a machine, talk to your authorized reseller." You lose all of the leverage that you have dealing with a real store.
Know that Apple charges resellers about 5% lower than the Apple store price for Macs. eBay takes significant fees, add to that PayPal fees. So anyone offering a machine at more than 5% off, there has to be more to the story than that. No authorized dealer is going to sell a new model factory sealed machine at a loss, nohow. There's just too much demand for them for that to make any sense.
It could be: a Hijacked eBay account. Stolen machine. Returned machine with defects. Old model machine that they hope you don't notice its not current. Or: No machine at all and it is a flat out scam.
EBay feedback means little: a hijacked account could have 1000 positive but you're dealing with a scammer, not the account owner. Or someone can run up 100 positives by buying trading cards and eBooks for $0.99 each, then once they have established their account, swing into bigtime fraud and then disappear.
If you insist on looking at eBay, remember that there are ALWAYS scams. You have a % chance of losing everything. eBay buyer protection has too many loopholes, essentially, they only protect you from sellers who are already honest and have a track record. Look at the seller's feedback. If there is a long gap between the last feedback and the most recent, then it could be a hijacked account. Ditto if the seller's prior items have been a totally different category of goods like collectible dolls, and then all of a sudden they have a bunch of 'new factory sealed Macs'.
Run away from any seller who even hints that the machines come from outside your country. Or who spins a story about the machines coming from an Apple promotional program, or from schools or orphanages or a developing country. These are fables - Apple doesn't discount. Period. And especially not for resale.
Congratulations for reading this far. Bottom line: Go visit your local Apple dealer, and look at the Apple store online refurb prices, and choose one of those. Don't get ripped off.