The secret ballot used in contemporary American elections inhibits a market for votes because there is no way to assure someone who pays you for your vote that you actually voted as you promised. That mechanism for preventing vote-buying is being undermined by the widespread use of absentee ballots, because voters can sell their votes and allow the buyers to mark the ballots and mail them in.
Absentee ballots are easy to get. Twenty-eight states allow voters to vote by mail-in absentee ballot for any reason, and most of the rest allow it when voters offer an excuse for their absence. Absentee voting is becoming increasingly common. This article reports that in a recent primary election, 37 percent of all votes in Dade County, Florida, were absentee ballots. The article notes that police and prosecutors are pursuing “a vote-fraud probe that has led to the arrest of two Hialeah boleteros, or ballot-brokers, accused of collecting absentee ballots from voters and in some cases fraudulently manipulating the votes.” Surely Miami is not unique in having a market for absentee ballots.
Elected officials have a big incentive to maintain the appearance of legitimacy in elections, because the legitimacy of the election confers on them the legitimacy of the office they hold. Could the increasing use of absentee ballots undermine the appearance of the legitimacy of elections, and with it the perception that office-holders have the legitimate right to hold their offices?
The possibility of vote fraud at the polls, in the form of votes cast by non-citizens, deceased people, and people voting in multiple precincts, has been on the political radar recently, but it appears to me that the potential market for votes created by absentee voting is likely a more significant factor in affecting the outcomes of elections.