I mean, that person actually got yelled at and had to leave the store. Some are more sensitive than others and just the fear of an unpleasant interaction is enough for some people. I've let small discrepancies slide just because the staff looked overworked and I didn't want to make them stop what they're doing, run down to the aisle and check prices and get their supervisor. For most I think it's just a time thing. It isn't worth a couple dollars to commit to an unpredictable amount of time going back and forth and waiting for a manager. I salute those lions like your MIL who stand their ground and fight back but there are also many, maybe most, who are just in a hurry or want to avoid confrontation.

Thanks, I appreciate your perspective.

One note about asking for a refund/price adjustment. Occasionally the store workers forget to pull the sale prices off the shelf when the sale is over. In these situations, the manager/workers are appreciative since they can pull the sticker that was left on by accident. Just my experience...