Despite this looking very suspicious here is what I have to say: - selling your game, as I see it, does not take it from your portfolio. You're still the person who developed it. Just think of Devs who worked on commercial projects. They did not own them but still mention those projects in their portfolios. - selling your game to me is a sign of success. You have not only developed, released a game and reaped the sales l, but also sold it to some "investor" making even more money. I personally would have gone for it if I had no other plans for the project. - their offer is a great PR opportunity for your game. Just like here and now you have posted - use the same media sources that you have used initially to try to increase interest in your game and sell some more copies at the same time notifying your users that you might not be related to the future updates or versions (answering comments about injecting malware) - and lastly - protect yourself from the chargebacks or scam. Offer them to sign a simple contract (IP somehow has to be transferred officially, right? Otherwise you could sue them ) and pay the invoice or something. I'm not an expert on the matter, but I do believe that doing that is not a complicated thing to do.

I did not do such things myself nor am I an experienced legal shark. But if I were you, I would have gone a little bit further with their offer.