This might not be the right hobby for you if you are overly concerned with how many got there before you, and when.

Overly sensitive providers (easily offended, that is), should STFU.  The OP has a valid point.  I once visited a provider that could easily be a 9 for looks (I never give 10s).  It should have been a great experience but wasn't.  The poor girl was was clearly sore.  She both limited the activities and rushed the session.  I had the distinct impression that she was being pimped out over-aggressively, as her price point was way lower than it should have been for a woman of her physical attributes.  I actually had to resist the temptation to call her back and urge her to get the hell out of whatever pimping operation she was involved in and raise her prices up to a level reflecting her looks, so she wouldn't need to turn high volumes anymore.

I've read on a few providers' sites that they only take one or two calls per day.

I know this is difficult but try to wrap your head around the following simple fact:  You will NEVER know how many guys your provider has seen before you on any given day.  If you enjoy yourself go back and see her again.  If you don't then don't.  

The ladies know what works for them and what doesn't. As a customer, over-thinking her side of things is foolish.

If you think they are, then you aren't doing the math.