As with any other profession, there are likely to be good and bad ones and I have seen examples of both. I once saw a "Marcel Marceau" dressalike in Paris, who had a crowd laughing uncontrollably for over 5 minutes, which in itself is no mean feat. Have seen many others who are good at what they do but one in particular stands out..who stood in a City Centre square with a crowd which was fluid...he was so bad that people were joining the crowd beacuse it was a crowd, realising he was rubbish and going...so many were doing the same that he seemed to have a large crowd...no-one was staying for more than perhaps a minute though. He probably thought he was great and I'm sure his Mum loved him.
Best wishes.