For sure the deal is done. Payment was sent. Merchandise traded hands. Done. From the legal perspective. Done.
Now, if this was a friend and in the names sake of keeping a friend it might be worth a sit down discussion. but in the eyes of the law, it's done.

I dont think it matters if he sold 2 games or not. There was a meeting of the minds. Product traded hands. Payment was made. End of story. Why would anyone see it any other way???

Wow! The balls on that guy. I'd be firm about it being a done deal now, no more nice guy.

This ^ for sure. Don't pay anything without the check back in hand.

Another pinside tip. I have an account I use only for writing checks (doesn’t get used often) but I only transfer enough money to cover the check, so the account is almost always at $1 so nothing to steal