How do I get off the list of potential clients that collection agencies call to solicit business?

I am unaware of any way to do so. For example, there is no business to business do not call list that I am aware of. Therefore, the trick is to spend as little time on the phone with these agencies as possible. An example of a way to end the call quickly, firmly but professionally would be to say something like this: “Excuse me, but we are not interested in doing business with another agency. Thank you for calling, and for your interest in doing business with us.” Follow this by hanging up without waiting for or listening to their response.

Taken from "1001 Collection Tools, Tips and Techniques" by Michael C. Dennis