It's quite straight forward; They don't charge extra because the prices are online and already given. They might not be as enthusiastic about sex with you rather than a handsome man, but there is no surcharge I've ever heard of.
The post hitting the nail on the head on this thread 
Its no different to other business sectors
Some customers receive a better service lots of reasons
Part of everyday life
Whatever it is as a customer you want to buy you employ techniques to tilt things in your favour
Given what SPs do its much more relevant & its not just looks [tho these help]
IMO you start laying the ground with the 1st text / WA & take things from there