I sell faulty material... (5)
I believe the answer is:
lisle
'material' is the definition.
(I know that lisle is a type of material)
'i sell faulty' is the wordplay.
'faulty' indicates anagramming the letters.
'i'+'sell'='isell'
'isell' anagrammed gives 'LISLE'.
(Other definitions for lisle that I've seen before include "Strong twisted cotton thread for the strange Ellis" , "(Fabric woven with) a fine cotton thread" , "Cotton stocking thread" , "Strong cotton fabric" , "Twisted yarn" .)