agent
broker
dealer
intermediary
intermediator
mediator
mercury
middleman
pander
procurer
negotiant
negotiator
treater
conciliator
diplomat
harmoniser
harmonizer
interpreter
make-peace
marriage broker
matcher
matchmaker
mediatrix
moderator
pacifier
peacemaker
reconciler
second hand
translator
appraisers
bosom-friend
confidant
consignee
counselors
dog
esquire
jobber
realpolitik
principal