As I wrote elsewhere, I'm leaving the door open for possible future friendship, however this is the best board under the general heading of "personal growth," hence this post.
When I went through divorce 20+ years ago, I saw an excellent T for 2 years. We did some great work and she helped me get in touch with and strengthen my own boundaries. She never did this by pushing me, rather through restraint. Any time I sought "direction" from her, which between my FOO and my ex-H I had a lifetime of receiving, she would adroitly turn the focus back on me so I had to keep reaching inside to determine what I wanted to do. This had a powerful and lasting effect, and since then I changed my family relationships and never let them or friends do a number on me, e.g. thwarted a half-sister's attempt at thieving etc.
Initially yelling was involved the emotions were much stronger and boundaries were more rigid. As time goes on, I'm more able to stay calm and focused, which helps me choose strategy and allow people I'm staring down to save face, and I can keep the essential boundaries fixed while flexing where it's comfortable. Also in professional relationships I've learned to to attain and steer resources on behalf of clients. Compartmentalizing maybe. I can push vendors hard and cut them loose as needed.
But some things are tougher, e.g. firing someone who works directly for me. A few times recently I've had to this and you know what, the sky didn't fall in.

Last time was yesterday. I had engaged an agent to lease and manage my home. She was by far the most thorough and detail oriented of those interviewed. Well once the contract was signed she slipped. She placed the ad a week late and didn't own that. Then she scheduled an applicant showing Wednesday and was a no show. I phoned her and she didn't apologize but insisted the appointment was for the next day. I checked the text and it was in fact that day. Luckily I was home, so I showed the applicant the place and vetted her. She gave me her records and we worked out terms and agreed on keeping direct contact, although I'm still having the agent run the credit/background check and prep the lease.
I had signed a contract obligating me for six months fee minimum, but it burned me to think that this agent had me doing her work. I dreaded the conversation but phoned her and called her out. (This might be easy for parents but I've never had a teenager

She owned her actions, apologized and agreed to release me early.
I've been able to do these things without feeling overly angry or disrespecting the other. Just, here's how I see you/your work and here's what I think is fair. What are you willing to do? And it's not only worked but each time it's easier so the emotions are a little calmer.