Sort of. There are some rules. Note that this varies by state as well, federal law is probably nonexistent. An old state law which for all I know was repealed

Sort of. There are some rules. Note that this varies by state as well, federal law is probably nonexistent. An old state law which for all I know was repealed ages ago or whatever was that an item couldn't be marked as on sale for half the year or more. You couldn't say it was 40% off for 300 days out of 365, that sort of thing. The easy workaround was to make it 40% off for three months, then have it on no sale at all but mark the sale price as the original price for the next three months, and switch back and forth whenever you want. So long as the item wasn't always marked "on sale" you were fine. I don't think the US has ever had real evidence based tests like that, except in major class action suit which have largely ceased to exist thanks to mandatory arbitration clauses.