It is complicated. The more STEEM (e.g. STEEM Power/SP) one has, the more voting power one has. If a blogger writes a great post, also he can vote on his own post with big self-vote (it is quite OK and rational as long as quality of post is OK) if he has large SP. Also, there are lots of advertisement for post through bot vote buying: https://s3.amazonaws.com/yabapmatt/bottracker/bottracker.html