Hiring an agent can make letting your apartment or selling your home easier and more practical. There are times, though, that some letting agents can cause more stress and be more of a pain than what they're worth. Don't let your hard-earned money go to waste on a bad agent-know when it's time to change your letting agent with these easy, fast rules.   * Think about whether your letting agent is worth keeping if a majority of buyers or clients start complaining about your agent and the way he deals with them. The buying or renting experience should be an easy and happy one for both you and your clients and your letting agent shouldn't turn this into a headache.   * You start disagreeing with your letting agent most of the time and he doesn't seem to listen to your thoughts or opinions.   * It's probably time to say goodbye to your letting agent if you find that negative thoughts about him start to obscure your judgment about your property and financial matters.   * Think twice about continuing with your letting agent if your requests aren't heard or delivered promptly.   * If your letting agent doesn't keep you updated on your properties, rent and tenants regularly then it's time to look for a new one.   * Have second thoughts about your letting agent if he doesn't reply to phone calls or emails right away. Proper etiquette demands that he be able to respond within 24 hours after a call or email.   You pay good money for a letting agent and it's only fair that you get proper and prompt service. Don't keep a letting agent if he falls below what is expected and what is in your contract with him.