In general, how many plates of food at a buffet does someone have to eat before the restaurant takes a loss?

I'm just asking generally for a "normal" buffet restaurant like Old Country Buffet or someplace like that.In general, how many plates of food at a buffet does someone have to eat before the restaurant takes a loss?
It would take alot for them to lose money as a whole, but id say 6 or 7 plates and theyve suffered a loss on one individual. it wont have any effect on their drawer at the end of the night though.In general, how many plates of food at a buffet does someone have to eat before the restaurant takes a loss?
Probably two and a half