There's a 100 different things to look out for when buying a MacBook off of eBay. Look at the sellers feedback and ask questions. Find out how it was used, what it was used for, and what condition the screen is in. If they don't discuss the body of the MacBook Pro, ask how it looks. If the price is too good to be true, then it probably is. There are some good sellers on there and generally the ones in mint or excellent condition command more of a price than ones that have been around the block a few times.
Honestly eBay is hit or miss. I hate when people describe things as "Mint" only for it to show up with scratches and scrapes on it. I swear some people don't know what "Mint" means. To me it means it looks brand new just like when it was opened from the box.
I purchased a 2015 about 6 months ago from a seller who described theirs as "In mint condition." When it arrived, it was dirty, had scratches on it, and had some nicks on the screen. When I questioned the seller over this his definition of "Mint" was far different than mine. He felt it meant that there were no dents in the body and that the screen had no noticeable scratches while it was on. While it didn't have either of those, there were two tiny chips in the screen and the outside of the MacBook had scratches all over it. I paid a little extra because of how he described it, and he was careful not to show any of the scratches in the listing. He refused a refund so I had to file a claim with eBay and easily won my money back. Point being, make sure you ask questions from the seller. I ended up just purchasing directly from Apple.
And from a specs standpoint, I'm partial to the 2.8GHz mid 2015 with External Graphics. Just my opinion though.
Good advise. What I'd like to add for OP is to always choose PayPal as a payment method with an expensive machine like this, never bank transfer. eBay has a fairly solid buyer protection, most of the time eBay sides with the buyer when the product doesn't arrive, doesn't match the description or (like in your case) has some flaws that the seller didn't feel like disclosing. But you need to pay via PayPal for this, as eBay has no control over whether or not the seller refunds you a bank transfer. Even when you run into a scammer who never even sends out a product, you're usually safe and will get your money bank as long as you took the safe way via PayPal. You only ever want to use bank transfer with sellers that you 100% trust (i.e. big retail chains who oftentimes also have a presence on eBay).
If a seller looks a bit scummy and only offers bank transfer as a payment option, then I'd never advise to take that chance. But if the seller looks a little bit scummy, has a really great offer and offers PayPal as an option, then it
might be worth taking that chance, because at best you took a great deal and at worst you have to deal with the hassle with filing a claim and returning it. Might. It depends a lot on the situation and how scummy the seller seems, but you almost certainly get your money back if paid via PayPal and being scammed.
Also, when I say PayPal, only ever as a buyer/seller transaction, never via the "Friends and Family"-option, as this bears the same risk as bank transfers for you as the buyer. If someone asks you to pay via this method, then it's always almost a scam. Also also, always communicate with the seller via the eBay messaging system so that eBay can read up on your communication in case of a conflict, not via E-Mail or other methods. And don't be afraid to open cases with eBay if something's not right, as there are set time windows during which you have to do this, and some fraudulent sellers play for time and hope they can hold you off with opening a case until eBay won't help you anymore. Give the seller deadlines and don't listen to excuses if something's not alright.
