That's a massive **** move and I do hope those guys get banned for that.

I've fought guild-invite spam using trade-window spam to counter-troll in certain F2P games, but shafting someone during normal gameplay when they've done nothing to you is utter bollocks.

Kind of unfortunate the busy trick is necessary, but at least its an option. My B-List is completely full up with gil-spammers that have never been dealt with, so that solution wouldn't be ideal, but eh.