<human>: Give me the gist of the text in a nutshell

Back story: I work and own a mom-and-pop restaurant (family business) in shady part of town. A lot of weirdos and creeps like to come in and try use it. However, I always deny anybody who is not a customer, although a lot of people manage to get through anyways (I don't want to get physical with anyone over it). This has also resulted in more than enough arguments. I am not rude in telling them when I am letting them know they may not use my washroom.

My worst incident involving the washroom, was a guy lied and said he had two friends coming to eat with him, and he rushes into the washroom. It's not abnormal for it to happen so I allowed him to use it.  Nobody comes in looking for him. 5 minutes later, I check up on him and I hear water in the background. Another 5 minutes pass and I smell smoke and still hear the water running. I tell him to GTFO or I'm calling the cops. He doesn't leave, and I call the cops, and as they come in to the restaurant, he's getting out of the washroom and they pull him outside to talk. He was definitely smoking something within the washroom.

So my questions are : Is it legal to deny people use of my washroom?
Is it wrong that I'm doing so morally? I just don't want to come in and see shit on my ceilings or have anything damaged/destroyed.
<bot>: Guy uses my washroom and smokes something in it. Cops get involved and now I question whether or not I am wrong with denying non-customers use of my washroom.