It seems the vote sellers are a bit conflicted now as they can be considered part of the problem by indiscriminately selling votes. Of course they cannot judge every post. I know OCDB operates a whitelist and others use various blacklists. Some do not do this and have been voting up some real crap as they have refused to pass any judgement. That may be good for business, but it is bad for Steem. There was an interesting discussion between some of them on Discord today. I did not hear all of it, but some posts may emerge.
Vote sellers have to accept that things will change. Users have more power to reduce rewards. I think those on this post are probably high enough and will not vote on it. I am low on voting power anyway.
The whitelist tends to be higher rated when they are handpicked on quality. Of course, once on things can change. The blacklist invites all and then removes for abuse after the fact, but as we have seen, abuse can go on a very long time.
Things are now changing for the better, I think.