Trick with void serial number (7)
I believe the answer is:
sleight
'trick' is the definition.
(I've seen this before)
'with void serial number' is the wordplay.
'with' is a charade indicator (letters next to each other).
'void' suggests removing the centre (the word is empty or void of its inside letters).
'number' becomes 'eight' (eight is a kind of whole number).
'serial' with its middle removed is 'sl'.
'sl' next to 'eight' is 'SLEIGHT'.
(Other definitions for sleight that I've seen before include "Dexterity (usually of hand)" , "Manual dexterity" , "It's deceiving to the eye" , "Artful trick" , "Conjuror uses this" .)