Jesus suggests that a good way to identify a false prophet is to look at their fruits. If “fruits” are just actions this seems somewhat obvious. What else would we look at? We can't see their heart, so of course we are going to look at what they do. Though perhaps Jesus means more by “fruit” then just actions.
If fig trees make more figs and grape vines make more grapes what do false prophets make? More false prophets. Some ferocious wolves may never bare their fangs, but, by nature, wolves travel in packs.
You can't always tell a person's character by looking at what they do in a given situation. But you can tell a lot about a person by how they influence the company they keep. Daniel