So a guy came in today and paid for a new tractor and bagger. He paid cash, cool, right? I didn't think much of it at first. Then I got to realizing that all but a couple of the bills were really old, like small faced 20, 30, 40+ year old bills. Without owning a fancy bill checking pen, can I check for validity? How far back were the strips placed inside the bills? Anybody know much about checking if they're real?