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.
A centralized DB will probably never happen. Different states can't even agree on collection laws.