In some states that would already be illegal with serious penalties. Like massachusset's grocers laws.

Iirc the law states customers are entitled to the lowest advertised price (including in store) and a discount or advertised price must be valid and available for 7days (maybe its more, i forget) and if its in print, have a clear start and end time, or its 7 days after last publication/ viewing- so if I see the tag in the store and they switch it out after I pick the item, it would have to be valid- price raises and end of sale tags are a thing eith the end date in bold on them. (Also meaning even if they run out early they have to give you a 'rain check' and honor it later when the item comes back in stock)

Penalties are triple the item price up to $20 off the bill at the counter, and thousands in fines and up to 30 days in jail for cashiers/ managers refusing to honor a price.

According to a friend who was the produce department manager at the local grocer, that wasnt the worst of it though- a report of failure to comply (ie a custome not getting the 3 the item discount at time of sale) could trigger a state's weighs and means audit, the first step of which is them forcing closure of the grocery store immediately for 30 days, which according to him litterally meant them showing up or having the local PD locking out employees to prevent a cover up- so no putting meat in a freezer, veggies back into the fridge, throwing out dieing product so It didnt contaminate the good stuff- basically guaranteeing a loss of everything in the deli and produce sections, easily a $50k+ hit even at our smallish grocery.