I have never found these policies especially useful, as I usually expect to do the background work properly and buy from the best place first time round.
I have always viewed them as only really useful if:
1 - I did not do my research properly, and discovered my mistake after the fact.
2 - It lets me leverage a benefit such as being able to inspect the purchase in a local store, or need it *now*. An example here would be Halfords who price match their website in their shops, and against other competing websites - at least for cycling products, or
3 - If there is some minor detail different that requires me to buy from a particular place.
Having said that I have just had my first success at this game (in addition to Halfords), when my door supplier, who has a liberal price-match policy, has just price matched a 10% cheaper price offer from Travis-Perkins for a nearly similar door and also the free delivery, and refunded £80. Nice night at the theatre coming soon :-).
Has anyone had any benefit from such policies?
(Note: agree that negotiating on the basis of "that price over there" is akey tool pre-purchase expecially for big-ticket items).
Ferdinand