I am not aware of such a website.
I have bought accounts from people going out of business before.
The first thing you need is to have access to all the stats. Then you need to be in touch with the program about it. If the program is not involved you can get taken, as I once did.
It can be profitable to do this, but you need to see stats over a good long period of time and preferably stats that can give you player data so you can estimate how long current players will be good for. Some people seem to attract short time players, some long term.
Also, some programs retain well, others do not. Last not least, if you don’t actively use the account and send new players, somehow, with some programs, accounts seem to dry up miraculously, even if before there were some very loyal players….other programs will retain the player for you for a long time.
It is a slippery slope. If you want to buy accounts it needs to be done with great caution. If you want to start a website doing so – it may be a good idea if you can find enough of them, do very thorough research and have a big fat disclaimer.
Personally, I would never sell an account. But I am open to buying them if they meet my criteria.