[theorique]

That seems to be a strange criterion.

The waiting tables example is "obvious", and while some activities are only compensated for a small elite (playing basketball, musical performance), there are a lot of activities that might be compensated and might not. Or be compensated indirectly.

For example, speaking at an academic or professional conference is "work", but it is probably not compensated (except possibly for a keynote or lead speaker). An author giving a book tour is work, but they are not getting paid for talks - instead, they may be "paid" in greater exposure for their work and possible increased sales.