A cranky agent? You're kidding! Haha... there are too many of those in today's market - but to be fair, it's a tough job practicing real estate these days. As long as you did not sign a Buyer Broker Exclusive Employment Agreement, you are free to go with whomever you wish. If you did sign such an agreement, contact your agent's designated broker and ask to be released from the agreement. And get that release in writing from the broker!
A general note to everyone out there... if you don't like your agent for whatever reason, or feel that your agent is being less than honest with you (it happens), you should fire them immediately and find a professional agent. Why not interview 3-5 agents and retain the one that impresses you the most? Don't use an agent just because they are your cousin, or your neighbor, or your Avon Lady. You should use the agent that will do the best job. Period.