If I backorder a domain that is expired and in redemption, does that guarantee that I’ll get it? Owner isn’t going to renew it. Says he doesn’t want it.
It doesn’t guarantee it at all. Actually GoDaddy is one of the least likely places you’ll get the domain. When domains become available for registrations (aka are "dropped"), whoever registers it first gets it. But there are companies out there that monitor these dropping domain lists and have computers that attempt to register them several times a second.
GoDaddy is one of these companies, but there are others as well. If you want to be sure to get it, you should reserve it on several of those sites. I don’t want to put links here since my account is new, but if you search for "how to snatch an expiring domain name" you’ll get a blog post from Mike Davidson where he lists those different companies and explains the whole thing a lot better.