I work for a company that subcontracts fixing POS (point of sale) hardware for large companies. My job is explicitly to confirm a system is faulty and either fix or replace it (if it is).

I don't owe the customer showing them how their hardware works, or helping them log jobs for their hardware correctly. All I owe them is making an effort to find a device that matches the fault and serial licated on my job, and fixing it if it a hardware fault.

But doing so helps reduce jobs being logged for functional devices (which are often cancelled after we expend resources, but before completing any billable work), and leads to more parts being logged (because I help them skip over useless time-wasting bureaucracy, as my knowledge is greater than their fiest point of contact).

So yeah, I don't owe them anything. Going out of my way like that is, on paper, a complete waste of time. But by extending that courtesy I help literally 100% of the stakeholders in that situation.

I'm reducing work for the store itself and their company's IT department, as well as reducing false positives being passed to the contract holder, leading to them and my employer wasting less resources. Even the store's customers benefit as logging a single job can easily take an employee 30-45 minutes (which is time take away from the store's already "streamlined" allocated hours).

Tl;dr: Not everything is a zero-sum game. Putting out a small amount of effort can benefit all stakeholders, even if it isn't explicitly required.