Purchaser's lower barn picked up (5)
I believe the answer is:
buyer
'purchaser's' is the definition.
(synonyms)
'barn picked up' is the wordplay.
'barn' becomes 'byre' (I've seen this before).
'picked up' indicates a 'sounds like' (homophone) clue.
'byre' is a homophone of 'BUYER'.
'lower' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for buyer that I've seen before include "A purchaser, maybe for firm" , "Caveat emptor - . . . . . beware" , "One forking out money" , "Shop employee" , "One making purchase" .)