Shop available to rent (6)
I believe the answer is:
outlet
'shop' is the definition.
(outlet can mean a shop or market)
'available to rent' is the wordplay.
'available' becomes 'out' (I've seen this in other clues).
'to rent' becomes 'let' ('let' can be a synonym of 'rent').
'out'+'let'='OUTLET'
(Other definitions for outlet that I've seen before include "Place of business for retailing goods" , "River mouth; shop" , "Discharge pipe" , "Store" , "Opening, vent." .)