"Plain folks" is a form of

propaganda Propaganda is communication that is primarily used to influence or persuade an audience to further an agenda, which may not be objective and may be selectively presenting facts to encourage a particular synthesis or perception, or using loaded l ...

and a

logical fallacy In logic and philosophy, a formal fallacy is a pattern of reasoning rendered invalid by a flaw in its logical structure. Propositional logic, for example, is concerned with the meanings of sentences and the relationships between them. It focuses ...

. A plain folks argument is one in which the speaker presents themselves as an

average Joe The terms average Joe, ordinary Joe, regular Joe, Joe Sixpack, Joe Lunchbucket, Joe Snuffy, Joe Blow, Joe Schmoe (for males), and ordinary Jane, average Jane, and plain Jane (for females), are used primarily in North America to refer to a comple ...

— a common person who can understand and empathize with a listener's concerns. It is like the propaganda, bandwagon. The most important part of this appeal is the speaker's portrayal of themselves as someone who has had a similar experience to the listener and knows why they may be skeptical or cautious about accepting the speaker's point of view. In this way, the speaker gives the audience a sense of trust and comfort, believing that the speaker and the audience share common goals and that they thus should agree with the speaker.

References

Propaganda techniques Deception Informal fallacies {{ling-stub