I think firm must leave someone in privileged position (7)
I believe the answer is:
insider
'someone in privileged position' is the definition.
'i think firm must leave' is the wordplay.
'think' becomes 'consider' (considering is a kind of thinking).
'firm' becomes 'co' (a firm is a company).
'must leave' indicates named letters should be taken away.
'consider' with 'co' removed is 'nsider'.
'i'+'nsider'='INSIDER'
(Other definitions for insider that I've seen before include "member of favoured group?" , "Person privy to information within an organisation" , "Member of select group in the know" , "person with confidential info" , "person in the club" .)