Good question. When it is @cheetah coming to your post, then its a bot; This robot analyses post and identifies plagiary (ie copy/paste from other posts or Internet) and sometimes gives suggestions for other websites with similar content. I suppose @cheetah is in development, since I know this bot as only checking from copy/paste, but now it also seems to suggest other sources with similar content. Another bot is @twitterbot, this one I think identifies when post is also tweeted through Twitter. More bots are on Steemit, like auto voters run and managed by Steemians.