Why don't e-commerce sites, e.g. amazon, include price timeline charts for their products so that users will be persuaded on the discounts? Does it incur any culprits for usability or even for sales? It sounds so tempting for a customer to check the previous prices of a product, doesn't it?
edit: To be specific, I hate the shops that apply anchoring effect/bias to customers. And I thought user satisfaction will skyrocket in the event that I can show the real price changes. But after all, this is the nature in commercial; making people feel happy out of shopping. Besides, as Vitaly outlined below gracefully, it might draw people into hesitation.