I have been doing this (Mystery Shopping) for quite a few years now, and have had some irate business owners during that time. I've always remained calm and let them vent. Then, I endeavor to explain in the sincerest way that every shop and its photos that I do are sent to the company where at least one set or more of eyes look at the photos and my answers.
But, OTOH, at one particular Exxon shop, the same employee each time would scream at me, "no photos, no photos!!!" when I would give him the LOA explaining as part of the site inspection, the company would like a photo of either the employee (not the face I would assure him) or a photo of the counter if he did not want his photo taken. I could tell his attitude disturbed the other employees as well as other customer. One man, a customer, even walked outside to ask if I was okay.
I would shrug and just leave the site, go across the street, take the required photos of a shop refusal and report it to the MSC. After a few times of his nonsense, I stopped asking for that station.
Fast forward months later, I decided to do the shop. I walked in and saw that same man. When it was time to do the reveal and present the LOA, he began shouting again. But this time, a person who I assumed was another employee just happened to be the site's owner. He gave the employee a dressing down in front of the customer and me. I assume it was a dressing down - it was in a language I was not familiar. The employee smiled at me and nodded. The owner apologized for the behavior. I took the photos.
The next rotation, I did the shop again - same guy, same obnoxious tirade. I reported the behavior and decided not to do the shop. Many months went by. On a whim, I decided to do that location again - it was bonused nicely. I noticed it would always sit there on the board - apparently no other shopper wanted to do it for the same reasons as I had.
The guy was gone! I've done that shop many times now. The miserable fellow has not been there. Maybe he was let go.