My Morrison's local adds money off stickers but the staff still have to enter the amount. Occasionally they forget or key in the wrong reduction.
I'm sure it's not deliberate as the staff have been there since before it was Morrison's and the manager is known by them to be a friend of mine so they would be really daft to try something like that.
To end on, here's a joke: why are Tesco profits falling?
Because every Lidl hurts