Google is centralized.
Well, there has to be a solution. Would voting system help? Several users will vote an alias down...
Actually, maybe a full-blown alias rating? For scammers, who don't trade honestly and stuff like that?
Something like a democratic Google Page Rank
It's a feature of client software (again) - to protect user from internet danger. Like child/parent control in AV software, white/black lists and so on. You can setup service and sell it to Nxt'ers, but it's not a part of decentralized Nxt network.