That's a store policy problem; it shouldn't be difficult for them to confirm that a payment has been made for the equivalent set of items within the last 5 mins, and even possible for them to cross reference with your card.
When I got stopped walking out of a supermarket with an item with an RFID tag on it, I don't think the security guard (who had no direct view of the self checkouts) even bothered to check that, just asked me to confirm the checkout that I'd used and roughly how much I'd paid for it. And sent me on my way with the advice that it might be a good idea to ask for a receipt when buying electronic items in case they were faulty and I needed to return them!
That’s the problem with the money incentive most stores have here - what I mentioned in the original post, that the security personnel receives 50 - 100 euros per “thief” caught
When I got stopped walking out of a supermarket with an item with an RFID tag on it, I don't think the security guard (who had no direct view of the self checkouts) even bothered to check that, just asked me to confirm the checkout that I'd used and roughly how much I'd paid for it. And sent me on my way with the advice that it might be a good idea to ask for a receipt when buying electronic items in case they were faulty and I needed to return them!