Should I work for free? -----> No.
Not even if they're your bestie, a charity, or your mother - unless you want an unpaid support gig from here until the end of time, or want to never speak to them again.
Free is not a sustainable dynamic for non-transient (I.e. Serving soup) tasks.
Imagine if you were to work in a soup kitchen as a volunteer, but the terms were that you'd be liable for any food poisoning, and you have to come in at 3am on Sunday because the stove isn't working, and someone there thinks you looked at the fridge once, which is close enough.