Based on an informal survey, the results seem to vary wildly from city to city. Some places, there’s a constant stream of ads which are reported and closed, so they’re probably prostitutes. Other cities (New York, for example), they probably SHOULD be reported and closed, but for some reason aren’t… they list phone numbers, they mention that they’re looking for “generous men”…
If you were also to peruse the listings of couples looking for men and notice the same images, chances are they’re legit.