Regular Mistaken for Employee

So a few years back I worked the tools section of a retail store and we would have this regular customer from a local mechanic shop come by probably every few weeks. This guy who we will call M would come in covered in grease, soiled gloves in his pocket and wearing a uniform of completely different colors from what our store. In short there really should've been no way to mistake this guy as an employee.

Anyways M was always nice to me and my coworkers but without fail every time he came in someone would ask him where something is or how to check the inventory for some item and he seemed to really enjoy messing with people who did that.

One day I'm working at the cash register checking out items for M and this lady comes in and instead of talking to me, the employee behind the counter who could actually help her, she goes to him and demanded M help her find something or correct some issue. At the moment I was looking down at the computer and actually started to respond figuring she was talking to me. But was quickly shut down and ignored. This lady had no interest in me because I looked young and inexperienced probably (I was only 18 at the time). After a second of trying to get his attention M just says "no" this woman confused and infuriated goes "excuse me what do you mean no?" to which M just "I mean I'm not going to help you and I'm not interested in it" at this point the lady is going ballistic. All attempts for me to try and tell her he doesn't work here fell on deaf ears. So she swore she would file a complaint about him and sue him legally. She asked to know his manager and M being the guy that he is said "go ahead" and even gave her his managers name and his own.

On a separate occasion I watched as a guy again seeing me and him goes to him and asks "can you help me find ..." M just plainly says "no" the guy had such a face of confusion and being dazed that I watched as he just kinnda walked out the store as if he was defeated. I honestly think M broke the guy, he just seemed so lost after that comment. The customer did come back a few minutes later with renewed confidence it seemed and this time came to me so I actually was able to help him

I'm not sure what it is about M that makes people think he works at my store. But I figure in some way M probably enjoys being able to give the responses all retail workers wish they could give to annoying customers. After all it wasn't his shop so he wasn't going to get in trouble and it's not his fault our customers can't read his shirt which had his auto shop's name embroidered on it.