If you're asking just because you want a general opinion, I have trouble voting either way. For all intents and purposes, they are female. Their breasts are probably fake, but then again so are a lot of providers. There's no uterus, but that alone doesn't make someone female (it's not like you're trying to impregnate them anyway). Genetically, yes they're different... but we're not talking about what the kids will look like or trying to rate someone's DNA under a microscope.
I've met gay men that were very feminine, to this day I still can't see RuPaul as a guy; the inverse is true of some women. Some post-ops are kinda obvious (Larry/Lana Wachowski), but a masculine appearance could just be genetics. With the advanced surgical procedures and hormone therapy, chances are you'd never know. Even the necessity for lube doesn't prove anything, quite a few providers rely on it despite being born female.
Essentially you're talking about combining two very small fringe groups: those that have undergone gender reassignment surgery, and those that get involved in escorting. I highly doubt there's much overlap in that Venn diagram, so I wouldn't let it keep you up at night.
I did some brief searches but couldn't find exact numbers of the number of surgeries done every year. Some say 40,000 have been performed since it got started in the 50's and 60's, others estimate 5-6000 per year without actual citations for where those numbers came from. Even if we inflate it to 80,000 so far, it's still a tiny fraction of the 300 million US citizens. (My searches also turned up a few post-op pictures, and they look pretty damn close to the real thing.)
Obviously there's no exact statistics on escorts, so I can't really compare that. But this process of gender reassignment is incredibly long, painful, and expensive. No offense to the ladies here, but I don't think there are too many cases where someone would purposely go through all of that in order to turn to escorting when it's complete. I'm sure it happens, but how many could it be? 1 in 100? 1 in 1000?
TER offers those options in the review submissions and search criteria as well as a TS board, hopefully people adhere to the rules appropriately. But if there's no mention in the ad or reviews and you still have some suspicions, please don't ask. There's no good outcome to that situation.