I had an associate that wrote an extensive order entry system that sat on top of a suite of applications for wholesale distributors. This was many years ago and orders typically came in over the phone. He displayed the remaining credit limit during order entry, and when finished the order taker had the option to hit a function key (old dumb terminals) that would start dinging the terminal bell. The order taker could say, "Hear that (places the phone receiver near the terminal which keeps beeping)? You're over your credit limit. I wish I could process your order, but the system just won't let me." Depending on the company, the order taker could press the function key again to stop the bell, and process the order based upon the promise to pay. Or place the order on hold and pass the call to AR. Adding a simple function key on a form to ring a bell, and nothing more, was a genius hack to a common payment problem.