Yes, most services or even independents will require screening via personal information or references by other providers.  I would suggest that you go with an independent provider on your first time.  Some agencies are often known for sending a girl other than what was pictured on the ad, pulling upsell moves to get more cash out of you, or worse.  Fully research the agency prior to booking an appointment.  There are plenty of reputable ones, I'm sure.  I personally only go with independents.  The girls who work for themselves see more of the money they make and I think it shows in what you get in the end.

A lot is made of references and the hassles associated with them.  My recommendation is that you look among the Korean providers and choose a few you like and call.  Most have bookers and, assuming you don't sound like a lunatic on the phone, many don't ask for referneces. Be confident, "This is ____.  I would like to see ______.  Is she available today."  You may get a few who ask who you have seen before.  Ok.  Give a few names of providers.  If they want to check references they will say so, and you know you have struck out on that one.  But eventually you will get through and and you will have not only the experience itself, but the refernece you need to give the next time.