Negotiator's intelligence evident in vacuous account (5)
I believe the answer is:
agent
'negotiator's' is the definition.
(agent is a kind of negotiator)
'intelligence evident in vacuous account' is the wordplay.
'intelligence' becomes 'gen'.
'evident in' means one lot of letters goes inside another.
'vacuous' means to remove the middle letters.
'account' with its middle taken out is 'at'.
'gen' placed inside 'at' is 'AGENT'.
(Other definitions for agent that I've seen before include "Double-zero-seven, for example" , "Vehicle" , "Salesman" , "Actors' manager" , "One employed to incite others to commit illegal acts" .)