Being quick to take in the tax people is a crime (6)
I believe the answer is:
piracy
'crime' is the definition.
(piracy is a kind of crime)
'being quick to take in the tax people' is the wordplay.
'being quick' becomes 'pacy'.
'to take in' means one lot of letters goes inside another.
'the tax people' becomes 'ir'.
'pacy' enclosing 'ir' is 'PIRACY'.
'is a' is the link.
(Other definitions for piracy that I've seen before include "burglary, in the main?" , "Robbery at sea or of copyright" , "theft" , "Copyright infringement" , "Crime" .)