[Archipelagia]

If you want to go thay route, it might be better instead to add a % to all the prices, and then at the end give it back if someone left a clean table. Something like "as a small token of gratitude for leaving the place clean and saving us time, here's 1% of your price back!"

One is punitive, other one is rewarding.

[conductr]

I agree and this is my main concern. Only issue I see here is the gamification only works if they know about it up front/before they make a huge mess. I guess I could put something at the table that explains why they should help out.