Try commercial incentive (4)
I believe the answer is:
goad
'incentive' is the definition.
(I've seen this before)
'try commercial' is the wordplay.
'try' becomes 'go' (both can mean an attempt).
'commercial' becomes 'ad' (abbreviation for advertisement).
'go'+'ad'='GOAD'
(Other definitions for goad that I've seen before include "Cattle prod" , "Act as stimulus - with pointed stick?" , "Prod with a pointed stick" , "Provoke, spur" , "Prompt" .)