This is a separate case and its not something you does regular than those of bounty hunters, whenever you notices a regular in and out of gas between addresses severally you should be able to detects that its a connected account. Although sometimes it could be is not one person controlling all those account but we need to be very careful whenever we are transacting and based on the forum drama we need to avoid sharing gas or btc between address to be free from this drama. There were other better ways to detects if the account belongs to one single user maybe constantly using same telegram id, facebook or twitter profile across both account then we can bold say such person are the owner of the both accounts and can be tag for cheating.