What you need shortly is held by farm vehicle dealer (10)
I believe the answer is:
transactor
'dealer' is the definition.
(I know that transactor is a type of dealer)
'what you need shortly is held by farm vehicle' is the wordplay.
'what you need shortly' becomes 'ans' (abbreviation or short form of 'answer').
'is held by' indicates putting letters inside.
'farm vehicle' becomes 'tractor' (I've seen this before).
'ans' inserted into 'tractor' is 'TRANSACTOR'.
(Other definitions for transactor that I've seen before include "A negotiator" , "Businessman" .)