John Lewis have this well-known boast, "Never knowingly undersold".
But that doesn't mean what you think it does.
I always thought that it meant "If we know that someone else is selling the same thing cheaper, we'll match that price".
But it's a bit different from the policy I thought.
It turns out that if you tell them about another retailer (they exclude online and mail-order) that's selling the item cheaper, they don't drop their selling price. They only drop their selling price to you, and give you a reference code so that you can claim that lower price. Which means that for all their other sales of that item, they are indeed, knowingly undersold.
I know about this because ladysolly is buying a washing machine, found it a lot cheaper else where, told John Lewis, and they offered her a price match. A John Lewis employee told me about the price match being valid and gave me the reference number. And I wondered why we would need a reference number, so I asked her, and she told me that they wouldn't be dropping their price to other people, just to us.
It may be that some people think that if you buy from John Lewis, there's no point in checking any other prices, because "Never knowingly undersold". But in reality, you do need to shop around, because their claim should actually be "We'll price match, but only for you after you tell us where you can get it cheaper".