I suspect Amazon gets around that by typically having most items "on sale". If an item's MSRP is $100, maybe Amazon normally sells it for $50 and shows it as being "50% off", despite that being the normal price. Then it goes "on sale" on Prime Day for $40, they change that to "60% off". Realistically it's 20% off, not 60% off, but I suspect they'd be clear of regulation against raising the price prior to a sale.