Facebook chat is one of the easiest ways to converse with our friends. To chat, other friends also should be online.
Interestingly, anyone can show us offline when they don't want to chat with anyone. Without any purpose, just show that they are offline but in fact, they are not.
The fact that they are offline, will may create misunderstandings if for a longer time. But to know whether they are really offline or online, you can check which of your friends are online but pretend to be online.
I have got some trick to find out who is really online and who is pretending to be. With the use of an app named "Online Now" will bring the list of friends who are presently online but appear as offline.
Go to the apps called as Online Now in Facebook. Before that check whether you have logged in to your Facebook account.
Check which Facebook friend is secretly online but appear to be offline.