Bird one may buy or part exchange (6)
I believe the answer is:
parrot
'bird one may buy' is the definition.
'parrot' can be an answer for 'bird' (I've seen this before). I'm unsure of the 'one may buy' bit.
'or part exchange' is the wordplay.
'exchange' indicates an anagram.
'or'+'part'='orpart'
'orpart' is an anagram of 'PARROT'.
Can you help me to learn more?
(Other definitions for parrot that I've seen before include "Raptor (anag.)" , "Repeat unintelligently" , "Mimic like exotic bird" , "Bright tropical bird" , "Spout" .)