I was in one of our local independents a few days back. The proprietor took over the business a couple of years back and decided to upgrade the systems in the shop. His background is 30 years in IT though IT is such a broad spectrum of skills and knowledge that this might be largely irrelevant.
Anyway, the payment technology based upon an ipad and an electronic card reader just wouldn't work. The fallback option of pieces of thin, flexible, partly transparent sheets of plastic and mainly round metal objects of varying sizes and colours was immediately instigated in it's place.
I don't know what the fault was but it didn't affect me as I had the necessary about my person unlike the other customer in the shop at the time who was the one being served when the issue first arose.