I often think about what might make voting more fair. Ideally we could have more people voting who are objective and neutral. And yet, we only want people to vote if they are an active part of the community. We do not want strangers to be able to drop in and start voting — they would disrupt the trust that builds up among the regular users of the site.
At one point I allowed any asker to vote on any question. That was vulnerable to abuse: an expert could set up a 2nd user account, ask a question for $5, and thereafter use the 2nd account to vote money to their 1st account.
I have decided to once again allow askers to vote. But the right will be restricted to the top askers: those who have spent more than $150 during the last year. The sum should be enough to deter abuse. And these are clearly askers who are active with the community.