Awfully strained buyer does it to upgrade (6,2)
I believe the answer is:
trades in
'buyer does it to upgrade' is the definition.
(eg trading in a car)
'awfully strained' is the wordplay.
'awfully' indicates an anagram.
'strained' is an anagram of 'TRADES IN'.
(Other definitions for trades in that I've seen before include "Hands over an object as part payment for a new one" , "'Hands over the old object in part payment for the new (6,2)'" , "exchanges" .)