In a world where exposure to untrustworthy communicators is common, trust has become more important than ever for effective marketing. Nevertheless, we know very little about the long‐term consequences of exposure to untrustworthy sources, such bullshitters. This research examines how untrustworthy sources—liars and bullshitters—influence consumer attitudes toward a product. Frankfurt's (1986) insidious bullshit hypothesis (i.e., bullshitting is evaluated less negatively than lying but bullshit can be more harmful than are lies) is examined within a traditional sleeper effect—a persuasive influence that increases, rather than decays over time. We obtained a sleeper effect after participants learned that the source of the message was either a liar or a bullshitter. However, compared to the liar source condition, the same message from a bullshitter resulted in more extreme immediate and delayed attitudes that were in line with an otherwise discounted persuasive message (i.e., an advertisement). Interestingly, attitudes returned to control condition levels when a bullshitter was the source of the message, suggesting that knowing an initially discounted message may be potentially accurate/inaccurate (as is true with bullshit, but not lies) does not result in the long‐term discounting of that message. We discuss implications for marketing and other contexts of persuasion.