I've been shopping at my local Iceland for a few years. When the cashier is doing her bit I am packing my shopping then present my card to the machine without taking any notice of the amount. They always ask "Do you want a receipt?" but I don't because it's just food (not, for example, an electrical item that might be faulty and need to be returned so I need proof of purchase).
OK so a month ago when asked if I wanted a receipt, on a whim I said "yes". When I got home for the first time ever I checked the receipt against the purchases and found I had been overcharged by a whopping £7. (Hamburgers were reduced from £7 to £3.50 a pack of 4 so I bought two packs but the till charged me full price.) It took me four phone calls totalling over an hour spread over a whole day to get the refund.
Since then I have changed my long-standing habit and have asked for a receipt every time, and I check the items as I pack them, and every single time I have been overcharged in some way. Sometimes because a special offer has not been input into the till, sometimes because I've been charged full price for something discounted with a sticker, other times I've been charged more than the price on the shelf card. The amounts I am overcharged vary of course, from 50p to £5.
Every time I hold up the queue and have people huffing and tutting and rolling their eyes and making rude comments whilst the cashier has to call the manager and wait for him to come then he takes a few minutes to sort it out with the cashier and whilst they are faffing about the queue is getting longer and I am seen as a bloody nuisance.
Today I was only overcharged by 65p and I started thinking that I should just let it go rather than inconvenience all those in the queue behind me.
Should I have a minimum sum over which I will complain, or go home then fight it out with them on the phone later?