It seems like that Steemit staff has thought about everything ! As the post says if you sell low your Power Up value will decrease proportionally as much as you sold so think twice before you sell ! Is it really worth it to drop the value of your posts and votes because you wanted to sell quick ? I don't think so. Just in case you didn't understood the mechanism, you have to know that if Steem price increases your Power Up, posts and votes value also increases !