Everybody has their reasons to take on the role. If you make no-/low-budget films this is important to remember — that camera person might want to try things out, that actor needs something for their reel, the sound guy might just want to make contacts in the industry, etc. If you manage to align your goal of making a film with theirs, everything works out.

Now if you don't let engineers live out their passion, you made the choice to select for the ones who just do it for the money. That can be a legit choice, but comes with risks.