Curse loud fools for being gullible (9)
I believe the answer is:
'being gullible' is the definition.
(I've seen this before)
'curse loud fools' is the wordplay.
'fools' indicates anagramming the letters (I've seen this in other clues).
'curseloud' with letters rearranged gives 'CREDULOUS'.
'for' is the link.
(Other definitions for credulous that I've seen before include "Likely to believe" , "Gullible" , "Apt to believe without sufficient evidence" , "Easily fooled" , "Too ready to believe things" .)