The transaction is moral if you pay what you think you would deserve for the same service.
Not when you pay as little as current conditions allow.
Interesting. As a full time electrical engineer, my hourly pay is significantly more than minimum wage. Therefore my hours are individually worth more than minimum wage. Therefore if I am buying a hamburger at McDonalds, the cashier and the frycook should both receive engineer pay while serving me, but receive minimum wage when serving a fellow minimum wage earner.
That would make an interesting accounting snarl.
And not be paid at all while serving the unemployed.