Cheggars (Charity Beggars) or Chuggers (Charity Muggers)
The con-man pretends to be raising money for charity by collecting donations. They get the mark to either give money there and then, or sign up to a pay monthly system. The con-man will just keep the money, not giving any to charity.
Commision Chuggars: This scam has a nasty cousin, mainly because it is actually legal. If you were to ask the con-man for his charity number, he would have to lie. Commission collectors actually do give money to charity, and have legitimate charity numbers. BUT they likely give less than 20% to the actually charity. The rest of the money goes to the organisation that runs the collection, and the collectors themselves (commission based).
Depends on how charitable you are.
How to be abode being scammed?
This scam can be stopped by a couple questions. Firstly ask for a charity number and check there credentials. Secondly, ask what percentage goes to the charity, and where does the other portion of the money go.
Final note, if unsure, just ask for information about the charity and find another way to donate.