Don't be taken in by his smooth talk; he's just trying to sell you something.

be 是系动词原形，在这里构成被动语态的结构。 taken 是动词 take 的过去分词形式，take in 这个短语动词的意思是"欺骗、使上当"。 in 是介词，与 take 搭配构成短语动词 take in，表示"欺骗"的意思。 be taken in 是被动语态结构，字面意思是"被欺骗"，表示"上当受骗"的状态。