An earl can be shifty, it’s true (4)
I believe the answer is:
real
'true' is the definition.
('real' can be a synonym of 'true')
'an earl can be' is the wordplay.
'can be' indicates an anagram.
'earl' is an anagram of 'REAL'.
'shifty it's' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for real that I've seen before include "Genuine, not imitation" , "Spanish football team" , "Actual, existing" , "Certainly no counterfeit" , "Working together" .)