Quack (9)
I believe the answer is:
charlatan
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">quack</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for charlatan that I've seen before include "Phoney" , "Person who falsely claims to be an expert" , "imposter" , "Trickster" , "Quack doctor" .)