Old drug dealer a hearty cop busted (10)
I believe the answer is:
apothecary
'old drug dealer' is the definition.
(I've seen this before)
'a hearty cop busted' is the wordplay.
'busted' indicates an anagram.
'hearty'+'cop'='heartycop'
'heartycop' with letters rearranged gives 'pothecary'.
'a'+'pothecary'='APOTHECARY'
(Other definitions for apothecary that I've seen before include "Drug supplier" , "dealer, old-style" , "Old-style pharmacist" , "Old-style chemist" , "Drug dispenser" .)