Recently, I sold a 2 year old MacBook Pro in good condition on eBay. The seller raised a fallacious case that it was not as described, and I reluctantly accepted a return. When the item was returned, it was a brick - would not boot. Upon opening the back, I discovered that the seller had taken out the 512GB SSD and replaced it with a 128GB SSD. It also seems likely, although I am not sure, that the logic board was changed as the Thunderport ports were misaligned on return. So, basically, the seller is a criminal.
I raised a case on this basis. eBay awarded the buyer a full refund. And, to rub salt in the wound, they charged me a total of £81 on top of that (reimbursement fee, return postage). So, now I not only have a laptop I can't sell, eBay feels it's OK to make a healthy profit from me being a victim of crime!
So, that's it for eBay. And also Paypal - a payment system that makes it far too easy for criminals to benefit from this kind of fraud.