>How do I negotiate with a minimum wage cashier, self-checkout, or a checkout page?
You "negotiate" by switching to a competitor, or in some circumstances refusing to purchase at all. It's a "negotiation" in the same way that participating in an auction is a negotiation.
I'm sure that's the econ 101 answer for healthy, theoretical free markets. In reality, we have market consolidation leading to near monopolies, collusion/price fixing between what few companies remain, etc. Refusing to purchase works for some things maybe, not so much for basic household goods and groceries, an area where a small handful of companies control the overwhelming majority of the market. Allowing survellience pricing just gives these conglomerates more leverage over consumers.