I had clicked through to Amazon to buy a book that cost about $13, ended up adding another similarly priced book, and was on the final checkout page with left mouse finger tentatively hovering over the buy button when I noticed this huge call-out at the top of the page:
Really? Then why isn't it! Seriously, the final checkout page is the worst place to be reminding customers that their cost could be much lower without offer a way to act on it immediately.
Didn't end up going ahead with it. It made the experience feel like being kicked in the nuts and laughed at for being so stupid as to pay the full amount. What they should have done is congratulate me for how much I had already saved over going to a brick & mortar bookshop, and then on the receipt page offered a tip for how to make my next purchase a little cheaper.