Post the link to the auction and I will check it out. I have quite a bit of experience both buying and selling on eBay and I can tell you if this is a "real deal" or a complete "stay-away". There is one MacBook Pro seller on eBay that I believe is buying machines and upgrading them himself, then selling them for a profit (for instance a $3800 machine, as configured from the Apple Store, advertised as new, he is selling for $2999). It is a MacBook Pro with 8GB of RAM and a 256GB SSD and a High-resolution display. It just looks too good to be true, but the guy has like 11,000 feedback and is a POWER SELLER. Also, nowhere he states that he has opened the machines and done these upgrades. It seems like you are getting the spec Apple config with Apple RAM and parts, which would make it much more expensive, but I think he is just getting the cheapest parts he can, installing them, and turning a huge profit on these BTO MacBook Pros.
I think his eBay name is "macman812" Yes, 11,382 feedback rating.
EDIT: I just sent a lengthy e-mail to this seller about this...I was curious whether he was selling Apple factory-configured machines with Apple genuine stock parts (hynix RAM and Apple Toshiba SSD from the factory), or whether he was upgrading these machines himself with his own parts. The deal just sounds "too good to be true"