The leverage is walking away and patronizing another store or online grocery service.

> As a society we don't benefit from min-maxing absolutely every opportunity.

Negotiation does take some effort, sure. But then again, you get to decide if it is worth the effort - Supply & Demand again is in play.

But you might argue "this is the only grocery store nearby!" I grew up in a small town. My mom never bought food in town. We'd drive 30 miles to the Army Base and shop at the Base PX. She'd buy 2 weeks worth of groceries at a time, because it was cheaper in the PX. My parents lived through the Depression, and were both very frugal.