Vote buying, i.e. cash for votes, happens frequently in many parts of the world. However, in the presence of secret ballots, there is no obvious way to enforce vote transactions. To infer effects of vote buying on electoral behaviour, I designed and conducted a randomised field experiment during an election in São Tomé and Príncipe. I follow a voter education campaign against vote buying, using panel survey measurements as well as disaggregated electoral results. Results show that the campaign reduced the influence of money offered on voting, decreased voter turnout and favoured the incumbent. This evidence suggests that vote buying increases participation and counteracts the incumbency advantage.