Guys typically choose providers by body type. There are other considerations that may weigh heavily, but the physical attraction normally has to be there.
Providers, on the other hand, generally take all comers (so to speak. They very rarely have pics of the guy; no reviews; and most don't bother to check references to inquire about the guy's fitness level or body type. (Again there are exceptions, but my experience is that most providers see that I have reviews and/or multiple okays on P411, and that's enough). I've always thought that the mental challenge of having sex with a guy who is not remotely physically attractive to them, must be one of the most difficult aspects of providing.
Conversely, I would expect providers to appreciate it when a client is quite fit. Yet it appears to me that is not necessarily so. I am older, but I work hard at keeping fit. I am surprised how many providers don't seem to notice or particularly care, if they do notice. Again, there are exceptions. A number of my ATFs through the years were providers who noticed my physique and commented appreciatively. (while other ATFs don't seem to much care or don't comment). It's an ego stroke when a provider finds you hot, and face it, a big reason hobbyists see providers is ego gratification. Still it appears to me that many providers simply do not care and in fact will say they do not care much about their clients being very fit; they only care that the client not be the opposite extreme.
Of course, this is entirely consistent with the obvious: Providing is a business for providers and the attractiveness of the customer and quality of the sex are secondary considerations. I'm sure there are many viewpoints and other factors, which I am curious to hear.