How Amazon uses the psychology of price:
http://recode.net/2015/01/13/how-amazon-tricks-you-into-thinking-it-always-has-the-lowest-prices/
I suspect the really clever part here – which the article glosses over – is how to know just which products will most influence customers’ assumptions about price. It’s easy enough to see which ones they click on most, but the ones with the most clicks don’t necessarily have the biggest role in forming price perception.
Supermarkets do the same trick with milk, as it’s a highly visible commodity which is easy to compare across competitors. Much harder to work out if Sainsbury’s multigrain bread is better or worse value than Tesco’s five-seed wholemeal loaf.