Returns policies.
People just assume that without a receipt they can just exchange or get a credit note with no questions asked. Wrong, I am going to challenge it. And if I do let you exchange it's only at the till value. Oh, look, it's £1, you definately paid £15 for it? ********. First off, if you did, you would be well out of your 28 days for returning it, because if something will never go into a sale from £15 straight to £1 (or in cases where it's half price rather than £1, we haven't had a sale in the past 28 days). Secondly, you have no proof that you paid that amount. Some customers at this point will then magically produce a receipt proving they paid full price, which then also shows they are out of 28 days. Again, exchange at till value. We have a returns policy, if you fail to abide by it, you lose out.
Of course there is the Matalan card, which keeps track of everything you buy, so we can in fact look up how much you paid. I have had, on several occasions, a customer return something without a receipt, claiming they bought it only a couple of weeks ago. It comes up on the till at a £1, they swear they paid full price. After a lengthy argument about us not having had any price reductions recently so I am 99% sure they would have paid £1 if they bought it when they said they did, I look it up on their Matalan card. The customer then is very embarassed and apologies profusely when it pops up on my screen, that they did in fact pay only £1.