While there isn't a 100%, always accurate way to check to see if a player is hacking, there are a few tricks you can use. Just for example, you can ask the accused player to type the phrase ".legit" in the chat. Most hacked clients use "." as there command key, just like the "/" key for legit players (Except hacks). For example, maybe typing ".m" would activate kill aura. So if they can't say ".legit", then they are using a hacked client that uses "." as they're command button. So again, there isn't a sure way to tell if a player is hacking, but there are a lot of small tricks that can tell you if the player is hacking or not. Your a wizard harry!