Pact is arranged about damage to drug dealer (10)
I believe the answer is:
pharmacist
'drug dealer' is the definition.
(I've seen this before)
'pact is arranged about damage' is the wordplay.
'arranged' indicates anagramming the letters (letters rearranged).
'about' indicates putting letters inside.
'damage' becomes 'harm' (synonyms).
'pact'+'is'='pactis'
'pactis' anagrammed gives 'pacist'.
'pacist' placed around 'harm' is 'PHARMACIST'.
'to' is the link.
(Other definitions for pharmacist that I've seen before include "Drugs dispenser" , "High-street chemist" , "Medicine dispenser" , "One who dispenses medicines" , "Drug dispenser" .)