What should I check before choosing affordable book publishing companies?

[rickymyers]

I'm getting ready to publish my first book and have been researching affordable book publishing companies, but it's difficult to know which ones are trustworthy. I don't want to choose based only on price and regret it later. What factors helped you make the right decision? Have you had any positive or negative experiences with affordable book publishing companies that could help someone new avoid common mistakes? Honest suggestions would be greatly appreciated.