See Past Product
You shouldn't hire any producer without at least having a good, objective look at past work created by that candidate. Work product simply speaks volumes with regards to the skill, knowledge and capabilities of the candidate. It also helps a hiring party get past all the fluff and sales talk that occurs during interviewing. If a person flat out can't cut it, that's going to be evident in the work sample or lack of it. And don't rely on work samples from the candidate alone. Look for work product that is already produced and available to see independently. That frequently is the most candid and best example of a candidate's skillset.
Get Qualified Referrals
The use of referrals can be a bit tricky since many candidate will be sure to have someone lined up to speak favorably for him or her. However, what a hiring a party should be looking for is a referral who is already well-known in the industry and established on his or her own merits. That person's opinion, even when favorable, is going to have a lot more weight. Successful folks have a reputation to maintain, and they don't want to be seen in the industry as being referrals of poor quality and garbage. So they too will be discriminating as to whom they give a referral for.
Don't make your hiring decision based on one 20 minute interview. Get personal with the candidate and spend some time with the person. The goal is to obtain a feel for what the candidate is really good at and has inherent knowledge of. That's going to become apparent in strong candidates who can carry an interview longer than five minutes. They can talk about their work, their education, their goals and most importantly, the lessons they learned from past pitfalls. You don't want a prima donna; you want a producer who is a worker and will get the job done by the deadline and is creative enough to tackle unforeseen problems on the fly.