Do more research here on PERB, and pick up on the names of AMP establishments that give HJs, BJs, and FS. If you go to one of these places, more often than not you wont have to ask at all. They'll straight up ask you, or just continue to go to work on you unless you say otherwise.
IMO, the whole "fantasy" of the AMPs is you being just a guy who wants a massage to work out a kink in their muscles, until suddenly she starts being all hot and bothered by touching you, that she starts acting a certain way and wants to escalate for an extra fee on top of what you paid for the room.... *Again, that's the "fantasy", the reality is everyone knows AMPs are blowjob factories; you know, they know, so most times they skip the foreplay part and get down to the business.
However, there are MPs that profess they 'don't' give extra service, but that entirely up to the masseuse, and you, and the confines of the room you're in; despite what the owner may/may not think. They don't want the reputation of being a full-service AMP stop, so their extra-offerings are kept low-key until something is said. The problem with gaining a reputation like that is having the City officials and even the cops putting that place on the radar, until they decide one day to raid the place. Like what happened in Richmond not too long ago. So if an MP's masseuse does take things further, it's done in subtle ways so you can prove to her that you are not a cop, or that what's about to go down is hidden from the parlour's owner that don't want that reputation attached to their establishment....and that makes the experience even hotter.
Assuming you're unsure about the establishment you're entering, then the key is really to pick up on the subtle hints given to you during the session, as well as setting the stage for yourself too....*the following is my experiences going to an MP and being unsure of the services.
1) Ask for the most amount of time, about 45mins to 1 hour. It shows you're a serious spender, and might be down for spending more if there are more to offer. Also it gives time to take up on any shower services made available. It's summer, you stink. And if you're down to get down, then it shows you care about health and hygiene to warrant consideration.
2) Read the room. Assume you're ignorant about the parlour you're in. "You're just a guy getting a massage", no extras are on the table (yet). Do not expect any sort of sexual act, nor actively pursue any sexual act.
3) Go Limp. When you're lying down on your front, have your arms to the side, slightly bent and relax your hand with unclenched fingers. Don't move, unless she's moving your limbs to better work certain areas. The reason for this, is to leave open 'access points' for her to brush up against. She's walking around the table, parts of her body is going to brush up against yours. Sometimes by accident, sometimes with a purpose. Like when she's standing adjacent to your waist area, trying to massage your lower back, and her vag is 'conveniently' pushing against your elbow or hand, almost grinding on it....that's kind of a sign, she's 'into you', or that extras are going to be offered... At this point, to ensure 'this is happening', you can pull away from the grinding and apologize; bodies are bound to touch, but 'not in that way', she's a professional, she'll understand. But what she does next will prove the intent. She either be more mindful of where her body touches yours (which could mean there's not going to be extras), or continue to 'tease' you like pushing her breast against the back of your head and she rubs up and down your spine, or grinding on your foot, as she's reaching and massaging your legs (for example)....
4) Do not willingly touch her on purpose. Her grinding on you is one thing, because she's initialing the 'act/sale'... But if you're getting grabby beforehand, then that could risk lead to a lot of misunderstandings and a lot of problems. Never assume at an MP you are not sure of, that you can just grab for her ass right away; again, there is a fantasy to be played out..... At best (still risky), stick out your pinky finger, and let it brush against her passing thigh and read on her reaction. At worst you'll get a warning, or horrible 'quicker service' to hurry you up and be done with you. Or she'll be professional, and move your arm out of the way, "so there is no misunderstandings".... or she'll take it as a sign to escalate, and more body grinding ensues, and perhaps get to the good stuff quicker....it's a chance things can go really bad, or really good; so let her make all the moves.
5) Conversations.... even if the language barrier is a problem, it shouldn't be too hard to pick out certain "key-words" to know where the session is going.
6) The legs... Most masseuse follow 'a script', and by the time they start working the legs that's probably the home-stretch of the session. She'll work your calves before getting to the upper and inner thighs. When she's working the inner thighs (despite what I said earlier about 'going limp'), spread your legs further apart ever so slightly to give her better access to the nether-regions. If she intends to upsell you for the extras, that's the point in time to see if she's committed to giving extras or not. As she's working your inner-thigh, ever so slightly she'll brush her fingers against your nutsack. You let out a sigh of approval, even tilt your hips outward for even better access for her...and if more fingers are touching your sack, then comes the fun part...
7) The flip and the offer... if she has your whole sack in your hand, up to the point she going for a total reach-around with the shaft, and maybe giving you 'the thumb'... it's basically 100% what's going to happen next, and the negotiating starts. Yes, you already paid for the room, but the next dollars to drop is going to be her tip and what you want her to do. She'll ask you to flip over on your back, sometimes with a towel covering your cock, and repeat the massage on the front part of your tights until she gets under the towel,... and that's when the offer is made.... handjob, or blowjob, or titty-job, or just straight up ride you.... agree to the price, and there ya go, the rest is obvious.
Again, all I've written here are from places I've been to where it's less than obvious. I do physical labour and drive a lot, so looking for a massage parlour is more of a priority for me than getting the goods; even ones that looks like a legit RMT sometimes surprises me with subtle hints for extra services. Otherwise, again, some AMPs mentioned on this website are pretty obvious, and most of the time the "courting" process is usually bypassed and go straight to business when you walk into their doors, where you pay the room fee and "the tip" upfront, get a light effortless massage, and then straight to the happy ending or other stuff.