You would probably select hair color, bust, age, ethnicity, body type, and see recent test results for STI tests. Then you'd probably get an estimates time when they'd arrive to your place.
It would be extremely interesting to see anonymous user data from such a service.
That said, I think the market for GFE and escorts is the future since legal prostitution means a general depression in prices so its no longer worth it to engage in what's actually a pretty physical activity.
> FOR those seeking commercial sex in Berlin, Peppr, a new app, makes life easy. Type in a location and up pops a list of the nearest prostitutes, along with pictures, prices and physical particulars. Results can be filtered, and users can arrange a session for a €5-10 ($6.50-13) booking fee. It plans to expand to more cities.