I have no idea of what these people were doing, nor do you. They were an everyday occurance wherever they were and I doubt that they could have survived very long if all they did was cheat people. Jesus was upset with them because they were conducting whatever they were doing in the Temple. Why the local religious authorities hadn't done anything about it for years, I don't know.
How can you say you don’t know what they were doing and then in the very next sentence, inform us of what they were doing and why?