> If I - and everyone else - could quickly identify which bank/gas station was acting in my interest without colluding, I would immediately switch.

I doubt this would be the case for most people for a couple of reasons.

First, gas stations are pretty transactional businesses that don’t rely on recurring customer relationships to stay afloat, it’s really all about the location. When was the last time you researched all the gas stations in your area and looked for the one that you felt served your interests above all the others? Nobody shops for gas this way.

Second, when gas stations maintain prices as their upstream costs come down to pad their margins, they’re doing so in cents per gallon, not dollars. A customer may save a dollar or two depending on the size of their tank, which isn’t enough of an incentive to stick it to the greedy gas station because you gotta be sure that the next gas station you’re headed to isn’t doing the same thing or costs even more. The gas station, OTOH, probably sees hundreds if not thousands of dollars in extra revenue per day depending on their volume for doing this.

> When was the last time you researched all the gas stations in your area and looked for the one that you felt served your interests above all the others? Nobody shops for gas this way.

I do. I own a classic(ish) car that both requires high octane gas and no ethanol. There's one gas station chain around that can be relied on to have it (in addition to every other fuel option imaginable). But I'm a relatively price-insensitive customer; I'd probably still buy from them at $5/gallon when others are at $2.50. Part of that is because of being happy with the chain, and part of it is anger at other chains for dropping non-ethanol options.

>it’s really all about the location.

Your claim is that the gas station has a monopoly over its location and is therefore able to engage in monopolistic behaviour and depend on consumer apathy - this does not really negate my point.