Agree with the advice above, in exchange for the service you have an absolute obligation to be spotless outside and for an inch or so inside. A soapy finger is good enough, don't need to douche or enema or anything extreme like that. Sweet Teen Julia will be happy to join you in the shower and show you how it is done.
I enjoy a talented tongue in my ass, and shave my balls, taint, and crack as far as I can safely reach. I used to wax (pro tip, do pay extra for the less painful hard wax) when I had a civvie friend who would really get tucked in, but don't any more now that I am seeing professionals and we do these things on a more transactional basis. Really any wg who claims rimming as a service will be fine with your unshaven ass as long as it is perfectly clean. But still, definitely shave your balls that's just good manners.