At the moment we are in situation where vote buying and selling is beneficial to both the buyer and seller but is damaging to everyone else around them.
I think the best solution is to offer better alternatives. Higher curation rewards and higher returns from DApps could discourage users from delegating to bots. DApps could use advertising to raise revenue and they could share this revenue with delegators.
Fontends could offer promotion services that actually targets an audience rather than just littering trending pages. After all, real content creators want their work to be seen by the right audience more than a few dollars out of ROI.