The root cause of the whole vote selling issue was STEEM's linear reward curve which made vote value predictable. Essentially turning votes and rshares commodity which can be sold as a service.

One way to destroy this whole market is to change the reward curve and making it impossible to know how much one's vote is worth exactly. @kevingwong detailed how this could be done in his post some time ago and it's something i recommend anyone and everyone to read.

https://steemit.com/steem/@kevinwong/are-you-seeing-the-truth-what-is-your-vision-of-steem

Now that @kevinwong is a witness on Steem, i'm confident enough that when he has what it takes to make a real change to the way Steem works when he has enough influence. If you haven't voted for him, you should!