If its a listing I will see which companies dominate the market. I will then call the manager and ask them would they would refer after I ask a ton of questions to match up personalities. I will always through in a ReMax agent. I send out three referral agreements and have my client (friend or family) hire the one they like best.
If it's a buyer I choose a ReMax agent referred by the manager and after I interview them to make sure the manager was right.