Unless a spam post has two votes and a big reward, it requires some work to identify henchmen and people are generally lazy.

Laziness kicks in before fear.

Somebody will come across the spam post, check the posting account REP:

• if low, they won't even bother to check the SP
• if high, as when the boss transfers SP to new account and posts with the old account, the SP remaining won't scare off downvoters