Because you can't prove a negative. I can never prove that you didn't pay something but you can prove that you have. As an agency, you're operating from a spreadsheet that Discover or B of A sends you. The consumer needs to keep good records until we get some sort of centralized database.
A centralized DB will probably never happen. Different states can't even agree on collection laws.
at 2:30 he states "anytime that somebody says that they've already paid a debt that you have in your make sure that you have them send you a letter and make sure you specify that you need a release letter..."
How about you prove that I actually owe the debt and then we'll talk.