[indecisive_user]

In the current system how do you sell your vote?

You go into the voting booth alone.

[drchaos]

"I give you $50 if you vote for me, you'll get it when I win the ballot"

If someone is willing to sell their vote in the first place, they have zero incentive to vote for another candidate. They only have to trust the buyer to follow up on his promise (which is required in any other scenario also).