I think some of you are missing the point. It is not a question of whether I should have known ahead of time how they do things, and it is not about anyone being right or wrong, or fair or unfair.
This is a question of pragmatics. The point is that the girl behind the counter kept hinting indirectly that I was supposed to go ahead and pay, but I completely misinterpreted the signals. She kept repeating the total and looking at expectantly, and it just didn't clue me in. I wasn't even thinking of the possibility that she wanted me to pay.
And I have been to this same office before, about 2 years go, although I don't have the slightest recollection of whether I paid that day before or after seeing the doctor. What I do remember is that after I saw the doctor and came back out to the counter, at the time when I would have expected to pay, they wanted to take my picture for my file, which was completely unexpected and very upsetting.
What I actually had in mind though was the doctor's office I went to most often growing up, and a different one I went to a few times in my late teens and 20s, and at both of those places you had to pay as you were leaving. I had a strong visual image in mind of both of those places, what the counters looked like and how I would walk up to pay just before leaving. So not remembering what happened 2 years ago, I thought back to those older memories and I had a very rigid expectation that this place would work the same way.
The question is not whether or not I should have known ahead of time, theoretically anyone could visit this office for the first time and not realize that it is expected to pay first. But I think most people would figure it out at some point. The question is, at what point does a normal person catch on to the hints...after the total is repeated twice? 3 times? Would the tone of voice clue them in? I thought she sounded oddly irritated or impatient, but I just figured she was in a bad mood. If my mother hadn't been with me to tell me, I wouldn't have ever caught on.
I'm surprised to see so many dismissive comments in this thread, though I shouldn't be, as it seems to be par for the course on this forum for posters to deny that other posters have legitimate problems. The fact is that I avoid going to a lot of places by myself because I have problems with this sort of thing, with figuring out procedures for how to do things and understanding what people are suggesting me to do, and it is very frustrating.