I always look at the ad and reviews of the girl and decide if she is worth my time. I don't assume she is busy unless she does not reply to my appointment request or tells me she is booked for the time I am requesting but could see me another time. There are a lot of fine providers in this area, many to choose from. Some are just not as responsive as others for various reasons, ie busy, have another job that limits their time and only see limited amount of clients, not interested in seeing older men etc.
Busy can mean different things. It can mean that she takes so many appointments in a day it's tough to control traffic or it can mean that she only takes a couple a day but is booked up for the foreseeable future. If it's the latter, that's a good thing. But if it's the former, who wants to be the fifth guy that day? But with a little research it's relatively easy to figure out which definition fits.