Avoid any sites offering to buy your Mac. These are mostly scams. They will quote you one price, but once it's in their hands, they downgrade that price and you either have to accept their terms or pay to ship it back to you. They aren't responsible for lost or damaged shipments either.
Try itsworthmore. That's where I've gotten the best prices. That said, I keep all my devices well protected thus I always click on the 'Like New' option when describing device condition. With all these places that buy devices they go over them with a fine tooth comb. Some will try to convince you that it's in poorer condition than it is. I always take careful and clear pictures before sending my devices away. In one case where they said there were small scratches, I took exception to their assessment. The sales guy looked at it then overruled the supposed tech who reported the scratches.