Lol
It's a number game I think, if you spend enough drunken nights in Nana Plaza one day your going to slip up.
I think I can tell them a distance now though I spend so much time amongst Asians it's quite clear to see between a real lady and a ladyboy, but many westerners have problems telling between them.
All I will say if I wake up next to one I will demand a discount for fraudlent advertising!