Financial scams have caused tremendous financial damage globally. In Japan, the police forewarn people by equipping them with scam-prevention techniques or providing awareness regarding examples of previous scams; however, this does not appear to effectively prevent the damage, as many scam victims do not remember these warnings when faced with actual scam encounters. Considering that scammers often use appeal to emotion techniques, peripheral processing during scam attempts might disturb people's abilities to recall the warnings on scammers' modus operandi, thus leading to failed counter-arguing efforts. We verified this hypothesis in an experimental setting by asking 162 participants to remember given forewarnings and resist deceptive advertisements. The results showed that participants gave the advertisers' manipulative intent a higher rating only when they processed the advertisement through a central route, in addition to being forewarned. This means that forewarning had no effect when participants processed the advertisement through a peripheral route. Moreover, forewarning recollection levels mediated the effect of processing route on this rating, which suggests that remembering forewarnings is necessary to generate counterarguments. This result expands the theory on forewarning effects and explains why people are susceptible to scam victimization. Furthermore, it provides implications for scam prevention.