Well, no-one can, this is kindoff the point. Mostly the post get's edited into noting or something totally different...
I'm not sure on the exact working, but I believe it works like this:
(in the case of posting pedo-stuff for instance or other terrible things) the steem community downvotes/flags the content. The post can then still be seen if someone want to by clicking show content/pictures (which is undesireble!!!).
The more effective way (that i believe is used by the Steemit.com -moderaters) they just choise to delink this post / not to show this section on the Steemit website (this means it still exists on the Steem-blockchain) but is not shown.
Can someone confirm this? Or am i totally wrong on the inner working on this?