Check your receipts!

Our local Coop is notorious for this. I always check any receipt from there and get a refund.

It's the backroom staff not keeping up with price changes; not usually the fault of the person on the till.

Yes, I do and am finding the same as you in several well-known high street shops. Assistants scan a more expensive item twice rather than another item, goods go through at the original price when they’ve been reduced, the till price differs from that on the shelf.
I often think it’s easier to buy a few products at a time to check the receipt, however a big shop in a German supermarket dealt with at speed at the checkout has yet to cause me a problem. I’ll take on board what you’ve said.

Both Aldi and Lidl have overcharged me on yellow sticker items and charged full price. I now always check my receipt before leaving the store

It happens quite often to me, so I take photos of the prices on the shelves to compare, especially with eggs.

Another time, a clothes shop wouldn’t give a paper receipt but instead wanted to send it by email, as it is their new policy but it would only be sent during the night, so I couldn’t see it immediately. When I insisted on seeing their screen, I found a two euros overcharge.

Also check the automatic till’s change, as I have been short changed before now..

I have always checked my receipts but I know that many do not.Just today I was over charged by £1 for an item at the till.
Not the fault of the assistant in this case, as it came up at that price.She put it right once it had been shown to be the case that it was indeed cheaper.

I always check my receipts and there have been discrepancies for the last five weeks at Tesco. I now check in the store and return to the shelf and take a photo of the shelf price so there can be no argument. Today it was swing bin liners priced at £1.70 but charged £1.85. Not much but every little helps which used to be Tesco’s slogan.
A few weeks ago I picked up a packet of doughnuts priced at 80 p on the shelf but £1 on the bag. It was explained to me that there were now 5 doughnuts in the pack instead of 4. Fair enough but why not change the shelf price ?It is still wrong five weeks later!

I have said before, when a shop assistant asks if you want a receipt, always say yes. If you don't you cannot know if you have been charged correctly.
Having said this, I went into my local Smyths toy store. I picked up 2 stocking fillers, Minion toys that had been reduced to £3. I took them to the till, the manager looked the items up, could not find them on the system, so gave them to me for free!!
I was so chuffed, but how decent of the manager to do this. So you can get treated more than fairly, sometimes, but this occurrence was certainly a rarity!!

I have noticed that when I get offers that should come off at the til at my local coop I don’t get them until I ask for a receipt.

I noticed in a London department store a few years ago that while the prices in the food department were unexceptionable, many of the comparative prices per litre, per kilogram etc. were wildly inaccurate. The member of staff to whom I pointed this out did not have a clue what I was talking about.

Check yhd prices against yhe weight/volume on the ticket below the items on the shelves,too!!

With a co-op card they send you money off coupons via an app every week, I sometimes find unless I scan my card first before you check out the items the discount is on isn't always applied but if I say to the staff did my discount come off? They say it can take a few seconds for the till and card to to match up. But following on from the OP yes it has happened to me in Aldi too, 30% discount on something I bought didn't check the receipt till I go home. Grr?