As others have suggested, referrals from friends, family, co-workers is the best source. If you are not able to get a referral, research which agencies are located in the area of the Berkshires you have an interest in. Call those agencies and get a feel for who answers the phone. If it "clicks" with an agent, ask them if they can act as your buyer's agent.
You might also puruse tte profiles of agents on Trulia and see if any stand out.
Please let me know if I can help.
Broker Associate, Massachusetts and New York
Berkshire Property Agents
Great Barrington, Massachusetts 01230