I hate when that happens. I almost walked out of a Rockville, MD spa after waiting 35 minutes. The mamasan came in just as I was starting to get dressed again. She was pretty attractive and had never given me more than a smile during several previous visits, but now she got very close to me, making nice with her hands (not THERE, though) and a kiss on the cheek, and asking me to wait just a little bit longer. I suggested she give me back half the house fee if I waited, and she countered with "I'll give you 30 minutes of 4-hand". I said 'well, okay'. I was curious how that would go, because I had gotten top-notch extras from my provider on previous visits, while the spa itself was legit enough to often have female customers coming or going when I was there. The promised 3rd and 4th hands were indeed provided by the mamasan, and while nothing too sexy happened while she was there, she did do some nice work on the glutes and thighs. When she bowed out, my regular attendant smiled and we did our usual stuff. By the time I left, I wasn't aggravated at all.
Bottom line--it sometimes pays to express your displeasure.
(Note--in the interest of accuracy, I can't remember if it was 30 min or 15 min of 4-hand. This was a little over a year ago.)