Sketch helps to show deficiencies (9)
I believe the answer is:
drawbacks
'deficiencies' is the definition.
(a drawback is a deficiency or fault)
'sketch helps' is the wordplay.
'sketch' becomes 'draw' (I've seen this in another clue).
'helps' becomes 'backs' (back can mean to support or help).
'draw'+'backs'='DRAWBACKS'
'to show' acts as a link.
(Other definitions for drawbacks that I've seen before include "Snags" , "difficulties" , "Disadvantages, hindrances" .)