eBay is easy to set up an account and get fair sales with. I sold my base launch PS4 for over $200 when the Pro was about to launch and frequently sell back games for near what I bought them for (if I waited till they were $30 or so)
As far as the question goes, I have my PS3 which is my PS1-3 library on it through physical or download. It sits in a drawer. I'll test out the BC with all the PS4 games I own and if it works fine then I'll sell the Pro on eBay