My example is about supply and demand, in particular if you are willing to pay a higher price than the supplier asks. Fungible or not doesn't matter at all, the only relevant factor for the discussion is the difference in price you are willing to pay and the supplier is asking.

Indeed, all business relationships are about trust. But they also are about business. I know of no other business relationship where the supplier expects that the consumer will pay him fairly. So what is so special about an employment contract, compared to all other businesses?