How can you tell the difference between products/services made by someone who makes said things out of the sheer love of making them vs. someone who only makes said things when compensated properly?

-- one word: QUALITY

I assure you that there are many things myself and others do well, some of which we like doing more than others, that we're absolutely not going to do if someone isn't paying me for it. Frankly it's one of the things that defines a professional--getting tasks done even when it becomes a slog or you're just not that into it.

How do you tell the difference in an interview or a medical consultation? We aren't talking about products.