In reality, it would be incredibly easy to tell the difference between people by even just using security codes or simply recalling events a person would have been told in confidential like the name of some guys dog or recalling when some dude farted in the matter transporter and stunk the place up, but I guess the problem with that is that the show would be over in about 15 minutes so these types of body-switch ideas never work. And then there's Shatner getting all 'flustered' as a woman which is a bit cringeworthy. Because it's TOS we will of course cut it slack, but it's pretty damned lame and maybe it's just as well the series ended when it did because they were running out of ideas but it really was a classic series despite a few turkey episodes.