How unpopular goods may be traded, making one puzzled (2,1,4)
I believe the answer is:
at a loss
I believe this clue is a double definition.
'how unpopular goods may be traded' is the first definition.
(unpopular items may be sold at a loss)
'one puzzled' is the second definition.
(at a loss can mean puzzled or confused)
'making' acts as a link.
(Other definitions for at a loss that I've seen before include "Completely puzzled, with no idea at all" , "Puzzled, bewildered" , "Nonplussed" , "makes one puzzled" , "How unprofitable business is run" .)