This is pretty fair and I stand behind it. I also have a different suggestion that might be controversial:
In the last game I played, players got weekly event rewards on the Friday after the event ended. That gave the devs time to investigate for cheaters, and most weeks several were found. This way, cheaters weren’t able to “steal” rewards and they didn’t have to worry about taking back things that’d already been spent, etc.
If things stay as-is, there’s subtle encouragement to repeatedly cheat, because even if you get caught and banned you get to screw someone out of a reward.