Didn't it used to be that at the grocery store, if an item is advertised on the shelf for a different price than what it scans for, they give you something like half the difference? But there's no code of ethics like that on the interweb.
Yeah in the uk I think if something is advertised at a certain price the shop has to sell it for that price - certainly happens fairly regularly at supermarkets
That isn't actually true. The price on the shelf is considered to be an invitation to treat. By taking the item to the checkout you are offering to buy it which they can reject. In practice they will sell it to you for the price on the shelf but this is not the law