Yeah, I've also found that having a great team lead and manager has been better than relying on a dedicated SCRUM master. (Beacuse my favorite SCRUM masters always take a promotion within a year.)

I do require my team to commit to and help me occasionally update a shared values document. I hate teams that don't have one. Teams have so many unspoken agreements that are genuinely easy to just write down.

That said, I say screw "accountability". I have the biggest paycheck on the team, so I can afford to keep the accountability to myself. My team has my back because I find them good pay and reasonable hours, not because of our of values document.