If you’re in the US I’m assuming you’d be considered an independent contractor, in which case they would provide an agreement and you can negotiate from there if needed. It should specify what happens if they’re unhappy with the result, like requesting revisions. But as long as you fulfill the terms of the agreement in good faith, I don’t think you need to stress about it.
Not even remotely a lawyer and only have a little experience writing IC agreements for a small nonprofit.