Hi,
That is not true. They said it is not against the rules but they don't encourage it. Please don't flame me all but as I see it you earn the credits and they belong to you just as your costumes or magic and you should be able to do with them what you would like including using them to trade for things you may not be able to get. New people may not have rare to trade but might be good in games and this is a way for them to be able to trade for some of the things they might not otherwise be able to get.
Just my opinon,
Bugdozer