I think your opinion on this subject depends on your personal experience. I've had some very reliable, dependable and caring online friends.
My least reliable friend? The guy I've been friends with since we were 3. We are still friends, but he has let me down a dozen times, sometimes quite badly.
Knowing someone IRL doesn't make them any more or less reliable. A reliable person will make a good friend online or in person. A unreliable person will make a less good friend.


