I for one appreciate postings that remind others of different going prices for items (though they should of course be accurate). If someone wants to buy an item at an inflated price, he or she is still free to. If I were shopping with a friend who saw an item and was interested, I would say something if I knew it were on sale somewhere else. Wouldn't you? Moreover, this is a site with an ethos of friendliness, courtesy, and cooperation (with some exceptions, such as this thread). Refraining from 'price policing' would harm that ethos, while courteous and accurate 'price policing' actually serves it.