Carlyn has good ideas!
When I go in to provide respite for a family as a volunteer, the client usualy balks.
I tell them that I am here for their caregiver, not for them, just to ease their minds.
When teaching (and parenting) I learned not to ask a question to which I expected a certain answer.
'Thank you for picking up that piece of garbage off the floor for me!"
–they would do it, then think about it, but I'd usualy catch them!
There are all sorts of tricks.
I was just writing about singing 'Oh, Canada' in classrooms. I would have the Gr. 8 kids who sang remain standing, and throw them a Hershey Kiss after. Bribery works, too! When the principal walked in he laughed.