This article only seems to refer to items bought over the internet, items bought in shops may be different. This is a relatively minor example but I was recently in WH Smiths and picked up a book that appeared to be part of a special offer, it wasn't, it had been incorrectly labelled but the assistant serving me honoured the sticker on the book, another one might not have been so inclined but I believe there is a proviso that stores must honour the label, although Quizmonster points out, if it's something like a car accidentally marked as �19.99, it is obviously a mistake.