Drove off with new merchant (6)
I believe the answer is:
vendor
'merchant' is the definition.
(I know that merchant can be written as vendor)
'drove off with new' is the wordplay.
'off with' is an anagram indicator.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'drove' with its letters mixed up with 'n' gives 'VENDOR'.
(Other definitions for vendor that I've seen before include "Person selling" , "Person who sells goods" , "Purveyor" , "One selling house" , "who does business?" .)