Person keeping watch finding appearance unacceptable (7)
I believe the answer is:
lookout
'person keeping watch' is the definition.
(I've seen this before)
'appearance unacceptable' is the wordplay.
'appearance' becomes 'look' (look is a kind of appearance).
'unacceptable' becomes 'out' (out can mean incorrect or inappropriate).
'look'+'out'='LOOKOUT'
'finding' acts as a link.
(Other definitions for lookout that I've seen before include "Watchtower" , "Person set to watch" , "Observer; concern" , "One who keeps watch, a sentry" , "Person keeping watch" .)