The way the system is designed currently there will always be vote buying/selling, it is simply easier for the wealthiest accounts to sell their votes and earn STEEM rather than create posts to earn STEEM or a combination of both...

The simplest thing to do would be to put a max cap on what a post can be upvoted to, this could be determined by average real world salaries. Once a post reaches max payout there is no reason to keep voting for it anymore... this would force the large accounts to spread their wealth more....

Would this solve the vote selling issue, nope but it would help...

Another thing that could be done is creating free voting bots to compete with vote selling bots, to become a member you would have to delegate X amount of STEEM power (which costs nothing because you can always undelegate) and to be a remember you can never buy votes from other bots. Once you got enough members eventually you would get more STEEM power than the vote selling bots... this would provide a consistent revenue stream for steady post creators...

Another thing that would help is anonymous downvoting, this would prevent retaliation, I am sure some people would abuse this but it would make it much easier to downvote people with large accounts who abuse the reward pool by getting large payouts for posts that do not deserve a large payout...

The STEEM blockchain works similar to the real world economy, the more money you already have the more money you will earn. The wealthiest just use their existing money to extract more money for themselves from the economy. The only way to stop that is to create rules/laws that create a more equal distribution of wealth...

I dont like vote selling accounts but I do use them sometimes, simply because the way the system is designed, if I don't use them someone else will and get that share of STEEM that was created...