An often-repeated theme on this forum is about how to discover if a massage shop you've not been to offers "extras" or if it is 100% legit.
Waiting for the girl to hint or touch you in a particular way might be too late in your booked time. Why wait to the last 15 minutes to find that she wants $50 or $100 to give you a HJ or if it is nude or not.

I am happy to read how other punters get to the point fast. In the meantime, here is what I do:

If I am at a new shop, I usually book an hour (sometimes 45 minutes). I don't start a huge chat with the girl, but around the 15 minute mark from start time, I ask her, "I want to ask you a serious question. Do you accept tips?"

In every case over the last many years, every girl understood what I mean -- none of them got confused and thought I am asking if it is OK to tip them for doing nothing more than a straight massage.

If and when they reply with something like, "Oh, yes. Why are you asking me this?"... I reply, "Because I am wondering what I will be able to get if the tip is $50 or more. What are you happy to do now with me."

Once the confirmation is reached about price/tips and services, I always say, "Can we start that part when we are half an hour away?"

I never liked to pay a tip for NHJ or HJ when all I have left is 10 or 15 minutes. Start early, and if you finish the deed early, she can always massage your legs or shoulders till your time is up.

How about you, fellow punters? How do you approach the subject with the girl?