The longer it was left, the harder the change would have been as by the time you had to drop them, the relationship was considered unsalvageable by all parties.

The longer it was left, the harder the change would have been as by the time you had to drop them, the relationship was considered unsalvageable by all parties. I think your boss should have taken more ownership earlier. Turning it around probably wasn't going to happen because it would have been a 180 renegotiation of how you related. To be fair, the customer also seemed to hustle you with a variation of "if you're a good guy, do me this small favour?" followed up with, "why won't you do me this next favour, I thought you were a good guy, now I'm unhappy..." and then leveraged the sunk cost you already put into the project to add incremental scope. The conversations I have begin with things like, "let's decide on outcomes and we'll get you there." Full stop. This is before you start working, because if you start working without an agreed outcome, your project is not delivering professional service value, it's being their employee. You're doing the favour. I get Agile is iterative with constant customer feedback, and this customer wanted a waterfall commitment process, but the job of your boss (imo) was to bridge those needs. It's great when a customer is happy, but that's the effect of providing value and solving their problems, happiness itself is not the job. I wouldn't worry about shouting matches, they're just a front. It's never the biggest dog that barks. Personally, I'm immediately suspicious of people who act unhappy because they only act that way because they think it works. So there wasn't a tactical change that would have made this relationship different, but there is a different way to relate in general that will ensure it doesn't happen again.