I am sorry you keep encountering this situation with therapists (though I am glad this one is giving you a refund). I imagine it's hurtful and frustrating. But keep in mind that a therapy relationship is a relationship, and that takes two people. No matter if something looks good on paper, you really don't know if it's going to work out until you meet and can reach a better assessment of one another in person. A diagnosis (or diagnoses) doesn't really tell a therapist anything about you as a person or how they're going to interact with you. If they don't feel it's a fit, that's valid, and they aren't obligated to see you just because you're giving money to them. Frankly I think it's good they told you they won't be seeing you early on instead of getting a few sessions in, when you're attached and feel trusting and vulnerable, and then tell you then. I know it hurts, but I think that, if it had to happen, it's good it happened this way.

As for telling someone you've been disappointed before and so you're hoping it will save you from future disappointment, that is not a given. I used to run into this problem with dating app matches: I had a bunch of disappointing experiences so I started telling new matches that I'd been disappointed before in hopes that our dates would be better. They weren't, most of the time. I know dating isn't exactly the same as finding a therapist, but both dating and therapy are putting yourself out there to form a relationship, and both can leave you hurt. My hope is that you continue to remain open to therapy and, hopefully, eventually you'll find a fit. Just remember: it takes both of you to make it work.