You will know whether a person is just a hireling or not by how she handles her tasks.
A hireling only sees the work as a transaction where she does the work she thinks the pay was worth. Just like ticking the boxes off a checklist, she makes the transaction happen without an extra.
But for a person who truly cares about the work that she does, she never just works when the boss is around. She works more than what was called for because she cares.
Caring about something goes a long way, whether it’s a job that pays or a work that regards others (be it animate or inanimate). And caring is not something you can learn from the books.