Can people see when you just delete their pm worth out reading it????

No because you will always read. Want to bet? Don't read this. See? Too late. You already have read. You can't control your subconscious like that

Just like in any other messaging system, You can only delete [b][i]your[/i][/b] copy of the conversation.. Nothing changes from their side

Nope. Once you send a PM what is done on the other side remains a mystery.

No. Well maybe if they're VIP I'm not sure.

They might because they don't try again

Nah