Holy shit, I was just thinking of this the other day ie. Escort service.
Like razorguns said the market is pretty much saturated, but to beat that you need to offer something unique.
1.You have to find the "liberal girls" the real slutty one's.That mean's repeat customers, and a good word of mouth.
2. most outcall escort services charge a flat fee for their escorts services ie. client pays $200-$250/hr, the girl will probably only see $125-$150 of that money. So you could take $75-$100 a girl per hour. So basically you'd be working volume instead of getting rich quick.
3.why would a girl take less money to work at an agency? Simple, Girls who work for agencies, obviously make less money. But that percentage pay's for advertising, security, drivers, a little gauaranteed money if she isn't getting alot of clients and bills are adding up, and general peace of mind.
A girl working alone who advertises online and in the paper puts her self at risk way more often, both physically and financially, more so then a girl who works out of an agency.
Also, it's important to treat the girls like royalty, as they are the product. An unhappy girl, can turn girls on you quick, and you could end up losing all of your good girls quick. No good talent= no money coming in.
One last thing, be prepared to recruit at all times, as your best girls will develop regulars ,and no longer need the security of an agency.