Yeah, every time you purchase a clip, you have to make sure you uncheck that "Yes, I wish to be added to this company's mailing list" check box. It's automatically clicked by default.
Have you been recieving newsletter emails from companies that you have NOT purchased clips from? If everything youre recieving is from a company that you bought something from, chances are, you just forgot to uncheck the box. If youre recieving stuff from other random companies that you've never dealt with, then thats a problem...