There's so much of it, there really is. That's why checking out which posts cheetah tags is incredibly helpful.
At the same time cheetah can't be everywhere. All it really takes is a few seconds with Google to see if something's been posted elsewhere for the most part.
If a post seems too professional, it's a good candidate to check out. If it's too formal, that's another good clue. Finally, if it reads like a news post, that's pretty much a dead giveaway.
Still, quite a few people on Steemit are professional writers, so you can't always rely on that. Sometimes you gotta go with your gut. If something seems hinky, do a little sniffing.