Involved in pricing product of castor oil seeds (5)
I believe the answer is:
ricin
'product of castor oil seeds' is the definition.
'involved in pricing' is the wordplay.
'involved in' indicates the answer is hidden within the clue.
'RICIN' is hidden in the letters of 'pricing'.
(Other definitions for ricin that I've seen before include "Castor oil plant toxin" , "Toxic protein from castor oil plant seeds" , "bioweapon" , "Poison from beans of the castor oil plant" , "toxic substance" .)