There's a reason why people are selling these sites so cheap. Do you think they would be selling a site for 50 bucks if it was to generate over 800 dollars a month (like the OP's proof of revenue)? No, they wouldn't. More likely the seller has noticed his efforts on building an affiliate site don't bring enough money so they try to make extra $$$ from selling these sites. I wouldn't say it's a scam, but don't expect to pay a little and start making money right away. If you hop on this bandwagon you have to work on the site: at least write unique content on the product pages, because if you don't, it will be close to impossible to rank.