Had a conversation with Skarlet about this and said I'd post some figures.
Important fact, you can sell common IO recipes at the shops, often for more than you can buy them from Wentworths or the black market. As an aside, the shops also buy invention salvage for common 250, uncommon 1000, rare 5000 which can be more than the going rate at Wentworths.
I've been doing this with lvl 45 and 50 recipes, both hero and villain side, and have made in excess of 300M (and spend 150 or so) across various servers not including infinity since I9 went live.
What you do:
Know the prices you can sell at:
lvl 45 lvl 50
Acc 43K 113K
Dam/heal 44K 116K
End redux/rech 41K 108K
Range 35K 93K
Imm/Sleep/Slow 32K 85K (slow is called snare)
Stun 33K 88K
TH buff/def debuff 32K 84K
Hold/run/dam res 29K 76K
TH debuff 23K 61K
Fear 20K 53K
Jump 18K 46K
Intangibility 15K 40K
Confuse 25K 65K
there are others but they're rarely available in quantity.
You can sell at any store in heroes, the basic QMs not the origin stores in villains.
So fill your CH inventory with bids for stacks of 10, and either sit there minding them, or go off and play while they're bought (or go to bed, last thing at night is a good time to set up).
I do this in KR for heroes and SH in villains as it's fairly quick to get between CH and shop.
It's not as lucrative as it was at the start, but expect to make 10-15K per enhancement, maybe a million or more each time you churn your transaction slots.
Mino