Turns down incentives including bit of nepotism (6)
I believe the answer is:
spurns
'turns down' is the definition.
('spurn' can be a synonym of 'turn down')
'incentives including bit of nepotism' is the wordplay.
'incentives' becomes 'spurs' (I've seen this in another clue).
'including' means one lot of letters goes inside another.
'bit of' says to take the initial letters.
The initial letter of 'nepotism' is 'n'.
'spurs' going around 'n' is 'SPURNS'.
(Other definitions for spurns that I've seen before include "Rejects with scorn" , "Rejects scornfully like unwanted suitor" , "Rejects with contempt" , "Rejects scornfully, say unwanted admirer" , "Rejects an offer" .)