MP = massage parlour. Massage parlours & agencies will accept blocked numbers or payphones. But there are also independents who will accept them as well.
If you have your heart set on seeing an indie who doesn't accept blocked/payphone calls, all you can do is research her reputation beforehand, if she has been around for a while & has positive reviews, she would likely never call you. Why would she? Then tell her, just to make sure for your peace of mind, to please never call you. Chances are she will be shocked that you would even think that she would do that. SPs are not dumb, nor would they ever maliciously call you just to out you to your wife or boss. Another thing you can do is, if you are doing an incall (& the SP doesn't require ID or a real name, most don't), is use a fake name, so in the highly unlikely chance that she ever did for some bizarre reason call you, she will be asking for the wrong name & it will be easy to say it was a wrong number.
There is also the possibility of borrowing someone's phone to make the call (a friend, a restaurant), & there are also many independents who will take bookings by email.
I know you think you have "too much to lose", but I honestly think that (as long as you stick with reputable well-known SPs) you have absolutely nothing to worry about. The SP has just as much as you, if not more, to lose, & many feel that not accepting blocked or payphone calls is just a small way to help protect themselves from the many risks that can come with this job. They do not do this so that they can call you.