What should you look for when choosing a ghostwriter?

Hi everyone, I’m thinking about using ghostwriting for an ebook project and want to understand what really makes the experience successful. I’ve come across many mentions of ebooks writing services, but it’s hard to tell what separates good ones from average options. Is it writing quality, confidentiality, or collaboration style? Has anyone here tried ghostwriting before and learned what works best? I’d appreciate hearing your insights and experiences.