Quite a few stores do similar as a gesture of goodwill, Dave. Best I had was a bottle of single malt in the local Morrisons. Marked on the shelves as half price, when it when through the till it scanned as full price. I queried it and, on checking, they said the half price sticker was out of date but, as they had not removed it, they gave me the bottle at the advertised price AND gave a refund of the full price! So, not only did I get a £30 bottle for £15, but they gave me £30 as well - company policy they said.

Needless to say I sent someone back in 10 minutes later but the half price sticker had gone:-)

DeG