Overcharge expert if tree is wrong (9)
I believe the answer is:
profiteer
'overcharge' is the definition.
(I've seen this before)
'expert if tree is wrong' is the wordplay.
'expert' becomes 'pro' (short for professional).
'is wrong' indicates anagramming the letters.
'if'+'tree'='iftree'
'iftree' is an anagram of 'fiteer'.
'pro'+'fiteer'='PROFITEER'
(Other definitions for profiteer that I've seen before include "one who makes too much in business" , "He charges too much in times of scarcity" , "One making excessive gains from trading" , "capitalist" , "insider trader?" .)