You never know. The profits are huge.
It may not be the proprietor, but the distributor/deliveryman bringing you cases of counterfeit rotgut that then gets served. Possibly, one of your barbacks is slipped some money to not look at the labels too closely. And for anyone who thinks the criminals can't do their own labels and capping on bottles to look like brand new hooch...
We've all likely been served fake booze somewhere or other, luckily, most of them just use crap ethanyl and not added methanyl.