Bargains rejected must include cancelled by-products (4-4)
I believe the answer is:
spin-offs
'by-products' is the definition.
('spin-off' can be a synonym of 'by-product')
'bargains rejected must include cancelled' is the wordplay.
'bargains' becomes 'snips' (I can't justify this - if you can you should believe this answer much more).
'rejected' shows that the letters should be reversed in order.
'must include' indicates putting letters inside.
'cancelled' becomes 'off' (similar in meaning).
'snips' backwards is 'spins'.
'spins' enclosing 'off' is 'SPIN-OFFS'.
Can you help me to learn more?
(Other definitions for spin-offs that I've seen before include "By-products or incidental results of larger projects" , "Incidental benefits" .)