Alot depends on teh circumstance and person you are dealing with. I have had to set boundaries with my Mom--food adn control are her issues. With her, I can't really say "these are the boundaries I have set up. Doesn't work! I just have to reinforce to her by words and actions what I will accept in behavior and what I won't. For example, she is in a nursing home, well cared for and has all she needs and more. But a few weeks ago, when I was getting a list of what she "needed" to keep in her room, one thing she requested was I stop adn get a dozen cookies at a local bakery. I just said "no". She pouted, tried the guilt card, " I don't have much pleasure in life..." that type thing, but I stood firm. Did I feel a twinge of guilt? Of course. Did I give in. No, because once I do, she has me in her control. My Dad faces the same issues and has more trouble setting boundaries, but they have been married 50 years, so I suppose old patterns are hard to break.
In any event, your gut will tell you what you need to do to stay sane. Follow it. It isn't wrong. :outtahere