Going off beam, taken in by confidence trick (8)
I believe the answer is:
straying
'going off' is the definition.
'beam taken in by confidence trick' is the wordplay.
'beam' becomes 'ray' ('ray' can be a synonym of 'beam').
'taken in by' is an insertion indicator.
'confidence trick' becomes 'sting' (I've seen this before).
'ray' put inside 'sting' is 'STRAYING'.
(Other definitions for straying that I've seen before include "Being bad" , "Drifters may be" , "not on target" , "Wandering from a direct course" , "Getting sidetracked" .)