I made a post about it. What if they are selling their votes for bitcoin outside of steemit? I couldn't get an answer or find one yet.

https://steemit.com/steemit/@sephiroth/i-ve-been-wanting-to-get-an-answer-on-this-what-s-to-prevent-someone-from-selling-their-votes-what-if-a-whale-sells-their-usd100