An easy test for this is how often the price at the register is higher vs lower than the marked price. If it's close to 50%, then ok, it's a mistake. But if it's higher...
I don't think you would reasonably expect it to be close to 50/50. Most price changes are increases and the mistake theory basically boils
down to the employees never updating the shelf tags. Which I think is an extremely plausible theory since the one employee at the store isn't paid enough to bother. And who's even going to check that they updated the tags? Dollar General isn't shelling out money for that.
There's another kind of store that's in a similar situation: thrift stores and nearly all
of them have also decided this problem is too hard. Lots of items are marked with just colors based roughly around their estimated value and the store changes the price/color mapping occasionally.
When we are in an environment of 3% annual inflation the day to day price movements will overwhelm the drift of inflation and be basically random in terms of increases vs decreases.
