[dyoqaazx] Vote buying and selling with a lie detector

A person sells their vote to a buyer.  But voting procedures are designed make it difficult for the seller to prove they voted according to the buyer's wishes: the seller cannot carry back from the polling place physical proof of how he or she voted.

However, one possible way which could work, which always could work, is for someone to sell their vote and then voluntarily undergo a lie detector interrogation to prove their vote.  The interrogation could include both a polygraph test as well as humans trained in spotting liars.  The "physical proof" that the seller voted according the the buyer's wishes is physiologically encoded in the seller himself or herself.  A vote buyer is interested in buying a great many votes, so even though a few people may be able to cheat a lie detector, statistically most people will not.

Of course, this process is very expensive for the vote buyer.  Can or will technology make it cheaper?  Cheap ways for people to prove they are telling the truth is something generically useful (a signalling mechanism in an imperfect information game), so there is demand for such a service beyond committing voting fraud.  We imagine something involving the fitness monitors popular these days.