There are lots of ways to tell, although very few are absolutely fool-proof (or stiff-prick-proof). Does the provider's neck show an Adam's apple? Is the person's voice low, husky, or raspy (vocal cords develop in such a way that hormones administered after the 20's have little effect on them)? Big hands? Breasts with smaller-sized nipples (and obviously a lot of ladies have small nipples)? Narrower hips and thinner thighs (again, non-POTs can be waifish as well)? Somewhat more prominent abdominal muscles (again, a very fit woman can have tighter abs than most men)? Is she overly heavily made-up, with enough eyeliner to do Cleopatra proud and enough face foundation to make her look photo-shopped?
When she walks, does she move more like an old-fashioned stereotype of a woman (think of Mae West's sashaying) than like most women actually walk?
Does the genital area look a bit . . . plastic-surgeried? Nature gives women (and men) a lack of genital symmetry. One of the labia may be noticeably longer, on that one side, than on the other side. It's not a problem, obviously, for, er, persons born into the gender, but for those who decide to have gender reassignment surgery, the typical request to the surgeon is, "Can you keep the labia short and even on both sides?" Actually, any POT who decides to have the surgery will probably insist that the surgeon fashion a pseudo-clit for cosmetic reasons, so perhaps the provider you saw simply had a very, very small one?
Incidentally, a lady's vag can feel different for a number of reasons, including following medically indicated surgery and (although more common on the west coast than the east) a vag tightening procedure.
I've opened the door of my vehicle on at least two occasions to an extremely sexy-looking streetwalking gal who immediately hopped in, spoke little (but sounded like a guy trying to sound like a girl), and - I know I'm not imagining this - cast me a glance which, in retrospect, was the look of somebody thinking, "Can he tell I'm a TS?" In one of those situations I found an excuse to pull over and let the now-lady out (although she demanded $20 for the time she was off the street). The other time I asked my passenger to let me see her breasts and vag. That SW was wearing a very heavily padded bra but I was immediately struck by how flat and lacking any curve or softness her stomach was. And she had wads of tissue stuffed into the crotch of her undies, so I couldn't discern anything below her pubic mound. She had a soft, low voice and I would swear a bigger Adam's apple than I have. I asked her to leave.
For what it's worth, if you've been in the hobby long enough . . . if you've made it a habit to visit Thai parlors or if you've ever limited yourself to quickie oral from SW's or B-page providers, you've probably been with a post-op trannie. I recommend you get over it. We promise not to tell your wife or girlfriend.
