"There's one way to find out if a man is honest - ask him. If he says, "Yes," you know he is a crook"

Groucho Marx's quote is a humorous method of mentioning the trouble of identifying someone's honesty. He suggests that if someone claims to be sincere, it is likely that they are not. This is because individuals who are sincere do not need to make such a claim. The quote suggests that it is impossible to understand for sure if someone is honest, and that it is better to be cautious when dealing with individuals. It also indicates that people who are unethical are more likely to make grandiose claims about their sincerity. Ultimately, Groucho Marx's quote is a humorous way of warning people to be careful of those who make claims about their honesty.