The art of persuasive speaking or writing (though often regarded as lacking in sincerity or meaningful content). this is called:

Rhetoric

Explanation:

According to my research on methods or communication, I can say that based on the information provided within the question this is known as the term called Rhetoric. Like mentioned in the question this is known as a way of communicating that has a persuasive or impressive effect, but which is often regarded as lacking in sincerity or meaningful content.

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i cannot see a paragraph to answer the question