Most agency owners will provide you with a reference if you were on time, a decent guy and didn't short the girl..

But if the provider has any specific question such as how big you are?  were you over all rough? what race are you?  were there any hygiene issues? Then the agency won't be able to answer the questions, since the agency owner probably didn't have sex with you..  

And believe it or not. Some providers really like to get personal in their reference checking.