Not sure if it works with everything, but i was hunting a pair of bloc stoat sunglasses and noticed Halfords have a buy 1 get 2nd half price offer on selected bike clothing. BUT..it seems online you are getting the second item FREE!! i reserved 2 pairs of stoats and it cost me £10 for the 2 pairs...these glasses are usually £30-40 elsewhere a pair!!
It prob wont work instore, but if you reserve online first you DONT PAY MORE than your confirmed reserve price.