Haggling has no point in a supermarket where the cashier's responsibility is maximizing throughout, and the streams of customers are thick.

Haggling works better at small shops with few customers and no lines. It allows the seller to have a huge markup on buyers who have little experience or time, or aren't as price-sensitive. It also allows for a human connection between the seller and a discerning buyer, and has an entertainment value for them both, like a short game.