Extremely tricky scam involving old business magnate (6)
I believe the answer is:
tycoon
'business magnate' is the definition.
(I've seen this before)
'extremely tricky scam involving old' is the wordplay.
'extremely' means to remove the middle letters.
'scam' becomes 'con' (I've seen this before).
'involving' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'tricky' with its middle removed is 'ty'.
'con' going around 'o' is 'coon'.
'ty'+'coon'='TYCOON'
(Other definitions for tycoon that I've seen before include "Wealthy or powerful business person" , "One very wealthy" , "Captain of industry" , "Magnate, wealthy businessman" , "top businessman" .)