There is another discussion that is worth having here, which is about the fact that this is not a mistake fare, but rather a coupon with insufficient limitations. European law does not give a retailer (of whatever kind) the right to cancel a contract/transaction simply because they forgot to add the conditions intended. This is significant because it legally differs from the 'mistake' fare. Mistake fares are prices that are wrong; under European law a retailer does not have to comply the consumer if he could have had the reasonable expectation that the PRICE was a mistake.
For coupons, this expectation does not matter. Here is an example from Belgium (200.000 euro worth of wood flooring for 25 euro) where the retailer forgot to limit the amount of coupons usable per transaction:
http://www.youtube.com/watch?v=8Upti...eature=related
or another example:
http://www.ad.nl/ad/nl/1014/Bizar/ar...r-1-euro.dhtml