Two were the same grumpy old man. The first one he refused to provide a key for the rest room and told me he was too busy for an inspection, and I should come back tomorrow. I responded that I didn't need him to complete the inspection and I can't come back tomorrow. I further advised him that I would take a picture of the counter and an overall picture and submit a report giving his name and description and advising he refused the inspection. He decided to give me the restroom key and allow the inspection. I returned to the same location a couple of months later and he recognized me. When I attempted to purchase a $1.00 item, he tried to charge me $5.00. It turned out he was in the process of selling the station and the new buyer stepped out form the service area and interceded, charging the correct amount. The new buyer apologized, explaining the situation and I proceed with my inspection. I think they made a movie about the old owner starring Jack Lemon and Walter Matthau.
The third shop involved an angry young jerk. When I asked for a receipt for my small in-store purchase he refused at first, angrily asking why I needed a receipt. When I produced the LOA he demanded identification. I declined telling him I'm here for a routine inspection or I could take a picture of counter and an overall picture and submit a report giving his name and description and advising he refused the inspection. That seems to work both with grumpy old men and young jerks.
I have always printed out color copies of the LOA, rather than images on my phone. That way the clerk has a copy and, I believe, avoids problems. I also wear a badge with my name and picture as well logos of the brand and Ipsos on my vest. But, of course, that is after the reveal.