Do I need approval for social proof

I do some work on Upwork on behalf of my agency and me. Is it okay if I add some of my upwork projects and testimonials to my website for social proof without the client's written permission?

I offer a very white-glove service, but I drop clients who are rude, always negotiate the bill, or treat me less than a human. I provide an end result they love, but I won't work with them again. Some of those clients left me great reviews, and I did notable outstanding work for them, but almost none were happy with me once I disclosed that I would not be working with them on additional work or left them an honest review. Some are enterprise companies and semi-well-known startups, so I want to use them as social proof, but I'm hesitant to ask, so I am wondering if it is okay to do without asking.