An uncle of mine managed a tiny grocery store, and gave out coupons for 50% off a total purchase of I think it was $100 intending to claim it was a mistake and was supposed to be 5%, hoping people would feel embarrassed enough to pay. There was no "seller not responsible for errors" clause. Now on the end of the purchasers, this was an "honest mistake." At what point does something cease to be an "honest mistake" and the seller stuck taking some responsibility for the error?
We don't know if the OP knew, when receiving the coupon, that it should have been 5%. The OP may have believed himself to be using a genuine 55%-off coupon. Should it always, without question, just go the direction of the seller? If a buyer makes some sort of error, the buyer's expected to pay. Why should the buyer also have to pay of the seller makes an error? If laws are based entirely on morals, then morally, even if by accident, if a seller misleads a buyer on a price, then the seller should be responsible. If I make an error and hit the gas instead of brakes, I pay, right? Because my mistake caused the damage.
