Instructed to use trade-in (7)
I believe the answer is:
trained
'instructed' is the definition.
(training is a kind of instructing)
'use trade-in' is the wordplay.
'use' indicates anagramming the letters.
'trade'+'in'='tradein'
'tradein' is an anagram of 'TRAINED'.
'to' acts as a link.
(Other definitions for trained that I've seen before include "Taught (a skill)" , "I daren't (anag)" , "Coached" , "Worked out" , "Schooled" .)