Smart chap I fancy is one running prescription-based outlet? (10)
I believe the answer is:
pharmacist
'one running prescription-based outlet?' is the definition.
(pharmacists deal with prescriptions)
'smart chap i fancy' is the wordplay.
'fancy' indicates an anagram.
'smart'+'chap'+'i'='smartchapi'
'smartchapi' anagrammed gives 'PHARMACIST'.
'is' is the link.
(Other definitions for pharmacist that I've seen before include "High-street chemist" , "One who dispenses medicines" , "Drug dealer" , "Drugs dispenser" , "Drug dispenser" .)