Lout smashed up alien shop (6)
I believe the answer is:
outlet
'shop' is the definition.
(outlet can mean a shop or market)
'lout smashed up alien' is the wordplay.
'smashed up' is an anagram indicator.
'alien' becomes 'et' (extraterrestrial).
'lout' anagrammed gives 'outl'.
'outl'+'et'='OUTLET'
(Other definitions for outlet that I've seen before include "Passage through which things can escape" , "Exit for water or steam" , "Retail point" , "Way of release" , "Opening permitting release" .)