Secondhand but found serviceable (4)
I believe the answer is:
used
'secondhand' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for used that I've seen before include "Second-hand; consumed" , "Sued, having been employed" , "Took advantage of" , "given employment" , "Accustomed - exploited" .)