Ignoring these things is how most such bussinesses are run. If you called the police, it'd cause a scene that would likely deter customers (and annoy the ones already there). You'd lose more money than you would get from the jerks in the end. That's not to mention the possibility of them deciding to cause havoc and break furniture or even assault the staff, or the fact that the scammers could simply deny your claims.
Losses like these are usually budgeted for and written off as a loss, with the police only getting called if the scammers make it a regular habit (where the cost of their repeated scams outweight the loss of causing a scene).