I tend to warn them and then report them to the site. The one player to a hand rule is usually what I point to in the message.
Its not always just a bored player or a angler,sometimes their skype went down or they are helping a friend in later position that is not answering back in chat.
It breaks down to about 50/50 from my experience in them knowing better or not.
Some have no clue they are breaking a rule. Like when the flop comes and they folded and state they would have had trips!