Retail problems put right by an advertisement (7)
I believe the answer is:
trailer
'an advertisement' is the definition.
(I've seen this before)
'retail problems put right by' is the wordplay.
'problems' is an anagram indicator (I've seen 'problem' mean this).
'put right' becomes 'r' (I've seen this in other clues).
'by' says to put letters next to each other.
'retail' anagrammed gives 'traile'.
'traile'+'r'='TRAILER'
(Other definitions for trailer that I've seen before include "Short scenes from a future film" , "An ad; one towed" , "Extract for advance publicity" , "commercial vehicle drawn along" , "Forthcoming-attraction ad" .)