Sure could be unsuspecting (9)

I believe the answer is:

credulous

I'm a little stuck... Click here to teach me more about this clue!

'unsuspecting' is the definition.
(thesaurus)

'sure could' is the wordplay.
'sure could' anagrams to 'CREDULOUS'.
But, I'm not sure how the anagram is indicated.

'be' acts as a link.

Can you help me to learn more?

(Other definitions for credulous that I've seen before include "Gullible" , "Easily fooled" , "Apt to believe without sufficient evidence" , "Likely to believe" , "Too ready to believe things" .)

I've seen this clue in The Globe and Mail.

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