Dodgy builder's tape is untrustworthy (12)
I believe the answer is:
disreputable
'untrustworthy' is the definition.
(thesaurus)
'dodgy builder's tape' is the wordplay.
'dodgy' indicates an anagram (a dodgy or wrong order of the letters).
'builders'+'tape'='builderstape'
'builderstape' is an anagram of 'DISREPUTABLE'.
'is' acts as a link.
(Other definitions for disreputable that I've seen before include "Superb detail (anag) -shady" , "Lacking public estimation" , "Not respectable, shabby" , "Dodgy" , "Infamous - shabby" .)