Fail to perceive finished appearance (8)
I believe the answer is:
overlook
'fail to perceive' is the definition.
(overlooking is a kind of failing to perceive)
'finished appearance' is the wordplay.
'finished' becomes 'over' (over can mean finished or ended).
'appearance' becomes 'look' (look is a kind of appearance).
'over'+'look'='OVERLOOK'
(Other definitions for overlook that I've seen before include "Disregard" , "Keep an eye on" , "Give a view from above - miss" , "Fail to observe or consider" , "Ignore a fault or have a view from above" .)