... who are sure to keep their prices fixed to one another.
As the owner of a medium size e-commerce site, I can tell you that most of the time that prices are fixed, it is not the fault of the retailers. Nine time out of ten, when you see every reputable retailer listing for exact same price, it is because the manufacturer has established a MAP (Minimum Advertised Pricing) policy where they will refuse to sell their product to any retailer who advertises their products below the MAP price. Most online retailers hate MAP as evidenced by our efforts to get around it by marking out prices, asking customers to create an account for best pricing, or not showing prices until the item is in the cart. These are all attempts to get around MAP policies which are instituted by manufacturers in order to protect their brick and mortar retailers by artificially inflating the price of the products online. MAP policies were illegal and considered price fixing in the US until a 2007 Supreme Court Case. More info http://en.wikipedia.org/wiki/Minimum_advertised_price.
You are always doing something marginal when the boss drops by your desk.