A player just reported that it's easy to play the full version of my (fully offline) Unity game for free by just:

1. Buy the full game.
2. Back up the data files.
3. Refund the full game.
4. Get the demo version.
5. Replace the demo's data files with the full version's data files.

I know that Steam disables refunding after a soft limit, so you can't just do this for every game...

But even so how could I defend against this? There must be easy solution for this, right?

Thanks in advance!