[webmaven]

Testing different prices on different days doesn't give you as much confidence (price sensitivity can vary by day of the week, weather, etc.).

Then there are tests that would be hard to run even on different days, like doubling your nominal price and splashing a "today only 50% off" or "buy one get one free" offer.

Real-world price testing is so much harder to pull off, it isn't as common, which is part of the reason web A/B tests seem jarring when the curtain is pulled back.