The old back in net showing unfavourable balance (5,3)
I believe the answer is:
trade gap
'unfavourable balance' is the definition.
'trade gap' can be an answer for 'balance' (I have seen 'negative balance' mean 'trade gap' so perhaps 'balance' could also mean 'trade gap'). I am unsure of the 'unfavourable' bit.
'the old back in net showing' is the wordplay.
'the old' becomes 'aged' (I've seen this before).
'back' is a reversal indicator.
'in' is an insertion indicator.
'net showing' becomes 'trap' (I can't justify this - if you can you should believe this answer much more).
'aged' in reverse letter order is 'dega'.
'dega' inserted within 'trap' is 'TRADE GAP'.
Can you help me to learn more?
(Other definitions for trade gap that I've seen before include "bit of business information" , "Imports/exports difference" , "That by which imports outvalue exports" , "Import-export concern" , "Imports minus exports" .)