Election campaigns are supposed to inform voters about where parties stand on policy issues. Yet campaign promises are not binding, since parties may advocate some policies in the campaign and implement others in office. This article thus analyzes the conditions in which voters believe party platforms. I argue that voters find platforms that can help the party obtain more votes to be less informative about the party’s ideology. This hypothesis is tested with both mainstream and niche parties in Western Europe. The analysis also distinguishes between governing and opposition parties. Empirical evidence for parties in opposition fully supports the argument: For mainstream parties, which have vote-seeking incentives to appear ideologically moderate, voters discount centrist manifestos. With respect to niche parties, which tend to lose support if they moderate, voters discount extreme platforms. Regarding governing parties, this article confirms previous work suggesting that voters disregard the platforms of incumbent parties. These findings have implications for democratic representation, party competition, and electoral volatility.