Fraudster may be seen by senior policeman as excellent (5)
I believe the answer is:
duper
'fraudster' is the definition.
(someone who dupes people)
'seen by senior policeman as excellent' is the wordplay.
I cannot quite see how this works, but
'by' could be 'per' and 'per' is found in the answer.
This explanation may well be incorrect...
'may be' is the link.
(Other definitions for duper that I've seen before include "cheat" , "Trickster" .)