Posting a job, interviewing candidates, and picking the right one is always a challenging process. I've been a hiring manager about 5 times for local positions, but that was easy. Hiring for a remote or offshore position is much harder. All of the conventional wisdom is useless when hiring for remote positions.
You get the bonus challenges of:
-Managing timezone differences
-Working thru cultural and language differences
-Verifying the authenticity of your info
-Dealing w/o back-channel references (usually the best source of info)
In the past 2 1/2 years of working with oDesk buyers and providers, I'd like to think that I've learned a thing or two about the process of interviewing remote contractors.
Post a detailed job description. Includes additional expectations about time of day availability, English skill, min / max hourly rates.
Send trial projects. Something as simple as "take a look at this website and give me 3 suggestions for improvements" are convenient little tests to see how they think.
Ask questions about attitude. Some projects will fail. What's important is how a provider deals with it. Ask about it.
Ask to talk to previous clients. They're still the best source of info.
Start small. Build confidence in your selection by starting with some small projects to make sure everything works out ok before diving into bigger projects.
Focus exclusively on responsiveness. It's easy to fall into a trap of confusing "responsiveness" with "responsibility".
Rush into a decision. Every one needs a project completed yesterday, but spend the time and energy to find the right candidates.
Mistake poor grammar for poor communication. "We are able to go for thing to make project completed" may be confusing, but ask yourself what's more important; reliable, consistent, honest communication or impeccable grammar?