This is a quick and dirty tip that Alex and I have started using to make sure Oliver keeps his promises and respects our deals.
We record him agreeing to whatever we want him to agree to. It's time proof!
So one night we recorded him agreeing to our terms and when he then tried to get his way (10 minutes later), we showed him the video. He remembered (and was actually quite surprised to see himself agreeing to it) and we avoided a power struggle. We have shown him this video many, many times since, and it always works!
What’s really important, in our experience, is mentioning as many details as possible and ask questions they have to answer (as opposed to making a video explaining the deal without the toddler being actively involved).
Give it a try next time you sense a power struggle is coming, it’ll work!