Like I said, I don't believe I've ever done it, as far as I know. I don't do very many requests. Though, I can understand the annoyance of it for very active providers now. Maybe an FAQ for people might help.
I'm not sure if I've ever done that, as the messaging system isn't the most immediately intuitive. Also, why are you complaining about people thanking you, wherever it may be? Seems a bit neurotic, honestly.