If you say that a person is trying it on, you mean that they are trying to obtain something or to impress someone, often in a slightly dishonest way and without much hope of success. They're just trying it on -- I don't believe they'll go this far
put on a garment in order to see whether it fits and looks nice; "Try on this sweater to see how it looks
If you try on a piece of clothing, you put it on to see if it fits you or if it looks nice. Try on clothing and shoes to make sure they fit