If pelf is involved, it's rubbish (6)
I believe the answer is:
piffle
'rubbish' is the definition.
(I've seen this before)
'if pelf is involved' is the wordplay.
'is involved' indicates an anagram (involved can mean confusing or complex).
'if'+'pelf'='ifpelf'
'ifpelf' anagrammed gives 'PIFFLE'.
'it's' is the link.
(Other definitions for piffle that I've seen before include "Rubbish, nonsense" , "Stuff and nonsense" , "rot" , "Balderdash" , "Informal nonsense, worthless talk" .)