A trick to gain a new model :-)
Anytime a friend asks me for a help, I say "YES, but you know, could you give me a favor ...? That way I have created several very cooperative models.
For example this guy needed to borrow a drilling machine:
And this one was very cold at a garden party, so I had offered him to share a blanket:
However, the best models are, of course, children. Give them something to eat, and suddenly you have got a very willing coworker :-)