Frauds involving bear? That's nonsense! (12)
I believe the answer is:
fiddlesticks
'nonsense' is the definition.
(fiddlesticks can informally mean nonsense)
'frauds involving bear?' is the wordplay.
'frauds' becomes 'fiddles' (fiddle can mean a fraud or scam).
'involving' indicates putting letters inside.
'bear?' becomes 'stick' (to stick with something is to bear it).
'fiddles' enclosing 'stick' is 'FIDDLESTICKS'.
'that's' is the link.
(Other definitions for fiddlesticks that I've seen before include "Rhubarb" , "Bilge" , "Bother!" , "Bows - nonsense" , "tripe" .)