If I'm right, this same issue showed up about a year ago with the same Casino and then went away. I'm not a lawyer, but would have to think that you are selling property that does not belong to you, or that you had the right to remove from their property. I also think if you ignore the email it goes away again. I can't see them spending big $$$ to stop you from selling a chip or two. I know that someone will say, "other Casino's don't tell you to stop". That does not make what people are doing legal, if it is illegal, it only means it's not a major issue.

My 2 cents

David