>It seems to amount to a similar principle, that their business model depends on repeat customers, and would fail if they lost trust.

You think dollar general is making $37.9B (in 2023) of annual revenue from one-off customers? Unless you're operating a tourist trap, or some sort of business that people only need a few times in their lifetimes (eg. real estate agents), most businesses rely on repeat customers.

No, I think they have other advantages that are less attractive to me.

I have money to buy in bulk, care about quality, and am willing to make longer trips to stock up. The membership is trivial relative to annual groceries.

I think think the target market for dollar stores is the opposite

Dollar stores around here pop up in small towns, killing off any locally-owned competition, and are far enough away from the big chains to mean they can charge quite a bit more while offering terrible service.

Note how they tend to have captive customers.