I think providers who work on a "first come, first served" basis are cheating not only you, but themselves, out of a pleasant experience. I know I certainly don't want a "revolving door" of people showing up one after another, or even worse, at the same time. Quality providers, in my opinion, reserve a special time just for you so that you can both be in the moment and truly enjoy one another's company. That's why, when you find one of these ladies, it's very important that a gentleman treats them with the utmost respect and appreciate the time and effort they've put into getting ready for your date.
Be sure to show up on time, and if you're running late (even 10 minutes) be sure to call as far in advance as you can and let the provider know. Common courtesy can solve a lot of things. I know a lot of providers who only wait 10 minutes for a visitor, and if they haven't heard from them by then, they move on...perhaps if they knew you were delayed slightly they might be more willing to wait a little longer.
I've never understood providers who say they are on the way to an outcall or give directions to their incall, and then magically disappear. It's incredibly rude to give someone the run around like that. I don't know how they stay in business, quite frankly! lol