Personally I just decline random invites and don't think twice. I've managed to erroneously send a party invite before too... But if someone was serious I assume they would say something first. As for communication in general, if you want better communication in your MMO experience you need to be the one role modeling it. Many times a quick tell to the person will clear it up. Or if the duty finder run is suffering from lack of communication, speak up constructively. Being on a PS3 isn't really a valid excuse.