If you're selling a home, you'll sign a contract with one agent, and you can't work with anyone else during the time specified in the contract (typically 90 days). If you're a buyer, unless you sign a buyer's contract, there's no law that you must work with one agent. Agents follow a code of ethics that preclude them from working with clients who are working with other agents, and it's also unethical for a buyer to work with more than one agent.