Dont be so sure he got it wrong BM, they arent all stupid, and may have thought you were an alright bloke, and it had been priced wrong, but let you get away with it. You are assuming that they care they sell the right thing at the right price. They dont, they just scan it and off you go
I got a £200 too chest for £30 in there because it was damaged. One of the bits was slightly bent so they couldnt sell it at RRP any more so let it go cheap. They could have gotten way more, but they just dont care