Damnit Joppo, now I have to shut down yet another of my key farming accounts. ;)
Seriously, all new folks should be given at least one polite notification of ninja rules when they breach etiquette. And I realise that some people see ninja'ng as another game, one which rewards the fast and vigilant with, well, rewards. But you are entirely right to be suspicious when people are hoovering (thanks Sachys) rather than just going after games they truly want. And I've heard tell that there are some supposed benefits to collecting a bunch of Steam keys, so perhaps there are grabs happening just towards that questionable end. If so, even more reprehensible.
Did I have a moral to all this? Hurm, yes, how about "don't kill the goose that lays the golden eggs". Something all ninjas learn, and all failed ninja aspirants do not.