Recently Smartsteem bidbot started blacklisting those who send them SBD/steem for up-voting if they find that quality is not very good and if post is not lengthy.
I was blacklisted because I sent them a bid for post which was not lengthy. The owner of Smartsteem named THEREALWOLF informed that they will blacklist if a post is not lengthy. In addition, they have informed in a post that the money sent by the blacklisted people will not be refunded.
It is really ridiculous to assess the quality by the length of the post. Rather, it is very easy to make long posts. Just copy a long post from somewhere and make some changes by inserting some comma or full stops, or removing some words or adding some gaps so that Cheetah will not catch you. But long post will waste the time of readers. So, Usually, I read a full article and make it very concise in a few sentence and post it. Those who read my article will get the message by spending only 10 seconds time. That is called quality. Quality cannot be assessed from the length of the post.
BE CAREFULL before using their service....Your money may be lost if they do not like your post.