O for a universal camelcamelcamel-type history of retail prices.
The original legal requirement for goods to have been on sale on Rockall for five minutes sometime in the last six years for personal callers only requirements have been so comprehensively worked around, we need something else. I suggest "retailers must show full price history of everything they sell and this must be as readily accessible as everything else on their websites" and even "and can be used by anyone else for any purpose they want". Hey - Gridwatch for retail!