alt Hacker NewsThe buyer in a grocery store can't negotiate; the store just sets the price and the buyer's only choice is to take it or leave it. Under the conditions described, the product is still worth it to the buyer who the store is charging the higher price (the one the store knows has more income and so can afford to pay more), at the higher price--there's just less consumer surplus. So the buyer still buys the product. But there's no negotiation anywhere; there's no opportunity for it.
The store manager has a lot of flexibility, and some of the staff are also empowered to take care of things.
If you feel you are being overcharged, see the manager. If you're nice to them, you can negotiate. Remind him how many years you've been a loyal customer. Being polite and friendly works, being a jerk does not.
The ultimate negotiating tactic is to explain your position politely to the store manager, and walk out.
I remember buying a car from a dealer. The dealer wouldn't agree to my price. He was adamant about it. So I got up, left, got in my car, started the engine, and backed out. The dealer came running out of the showroom and said he'd match my price.
Businessmen will always tell you that prices aren't negotiable. That is a tactic for rubes.