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')
'the salesman say when faulty' is the wordplay.
I cannot really understand how this works, but
'salesman' could be 'rep' (sales rep) and 'rep' is found in the answer.
an anagram of 'say' is 'ays' which is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'to' acts as a link.
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" .)