Final answer:
Marketers should consider expertise, trustworthiness, and attractiveness when selecting spokespeople to maximize message influence. These attributes contribute to the credibility and persuasive power of the spokesperson.
Step-by-step explanation:
The three categories of source attributes that marketers should consider during the selection process, according to Herbert Kelman, are expertise, trustworthiness, and attractiveness. These attributes are vital because credible speakers, or those with expertise, are more persuasive than those seen as less credible, and trustworthiness enhances the reliability of the message conveyed. Additionally, physically attractive spokespeople are often more persuasive than less attractive ones, leveraging societal preferences and biases towards symmetry and certain facial or body features that are culturally viewed as appealing.
However, the overall impact of a persuasive message also significantly depends on the credibility of the messenger, where factors such as honesty, bias, rationality, well-informedness, and clarity come into play. It is essential for marketers to select spokespeople who can resonate with the target audience and trigger interpersonal communications, thus potentially leading to behavior change.