What should authors check before choosing a book publishing service?

[rickymyers]

I’m preparing my first book and researching a book publishing service, but I’m unsure what really matters beyond the advertised price. How do authors compare editing, formatting, distribution, royalties, rights, and contract terms? What questions should I ask before signing anything, and which warning signs deserve attention? I’d appreciate serious, honest suggestions from experienced authors who have used publishing services and can share what they learned.