Gives back to the salesman, say, when faulty (6)
I believe the answer is:
repays
'gives back' is the definition.
('repay' can be a synonym of 'give back')
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for repays that I've seen before include "Returns money loaned" , "Recompenses" , "coughs up again" , "Settles debt" , "Returns loan or favour" .)