I suspect that by and large these people actually give themselves away. They do this by looking around to see who is watching or staring at them, making eye contact with the general public. This is just not natural, only the suspicious, the dubious among us do this. One of the ways shoplifters are spotted is because they look shifty, checking if they are being watched, and security cameras or in-house detectives can see this. The general public are usually far too preoccupied with their own problems to be bothered with looking for unusual passers- by.
Height is a perennial cause of complaint.
Yet there are still natural women who are tall. They are used to being tall, it is normal for them, and they just get on with life. They may not like it, but they do not consider being thought of as a man in a dress. A friend of mine who was very tall complained that men expected her to carry suitcases, for example, and never offered to help her, which she did not like, but they never considered her 'masculine'. The requisite for modelling is that the girl be tall, so it can be considered a considerable benefit.