If its a man turned to a women, the way women move, what they do and talk is so different from men, unless you want to be fooled you would know.
I've never met a transsexual but I'd imagine that a man could become a convincing woman if he worked hard enough at it. You wouldn't spend months taking pills and having surgical procedures only to continue to walk with your legs splayed, talk like a geezah and fart recreationally.