There is no rule to say you must reply to every message, however, it is polite to reply to a genuine message. If someone has taken the time to send you a pleasant message then a quick reply is courteous. If you’re not interested a short ‘thanks but no thanks’ message is sufficient and usually appreciated, but it can sometimes trigger an unwanted response asking why you’re not interested. In this case, it’s best not to get dragged into a debate. Just because someone chooses to send you a message doesn’t make you obligated to reply. Some people assume no response means you’re not interested, but others will see it as rude. It’s entirely your choice whether you reply or not. If you do reply but start to receive abusive messages, block that particular member and report them.