On one occasion I paid for my goods in the shop then remembered another item and went to get it - the shop was otherwise deserted so I just left my bags at the checkout (avoids suspicion that I've added something to the bags). When I returned with the additional item the manager (who was running the checkout) said I hadn't paid for the rest of the goods and would have to pay before he would let me leave. Needless to say I did leave with my goods and didn't pay again, but it was a fairly unpleasant few moments. He knew exactly what he was doing, and did it deliberately. I've rarely been back there since, even though it's my closest shop.