I'd upset a client just the same (9)
I believe the answer is:
identical
'just the same' is the definition.
(I've seen this before)
'i'd upset a client' is the wordplay.
'upset' indicates an anagram.
'a'+'client'='aclient'
'aclient' with letters rearranged gives 'entical'.
'id'+'entical'='IDENTICAL'
(Other definitions for identical that I've seen before include "Not any different" , "Exactly alike, the same in every detail" , "Aid client to be the very same" , "Indistinguishable" , "not distinguished" .)