How did you go about making this?

[RibbonBlue]

I was thinking randomly, could you have sold this game on your own?
Do something like:
Purchaser uses paypal to pay you X cash.
Keycode is sent to purchaser
purchaser types in keycode at your website which then allows him to download your game.
Keycode is removed from the list of keycodes that can be used to download games, and the list from which a keycode is given to the purchaser.