Why did black beauty call Alfred Smirk a humbug?

Black Beauty called Alfred Smirk a humbug because he was a deceitful horse dealer who pretended to be kind and knowledgeable while actually being dishonest and exploitative. Smirk's behavior, which included mistreating horses and prioritizing profit over their well-being, revealed his true nature. Black Beauty's use of the term highlights the contrast between Smirk's façade and his unethical practices.