Smart
King
Commercial trait increase OCN to 125% from default. So we will get 25% less rank corruption.
OCN on standart map is 20. Deity level cut it to 12 (or 15 if commercial).
Rank corruption for cities with rank = 1,2,...,5:
1 >> 0.042
2 >> 0.084
3 >> 0.126
4 >> 0.168
5 >> 0.210
With commercial trait:
1 >> 0.033
2 >> 0.066
3 >> 0.099
4 >> 0.133
5 >> 0.166
Corruption difference = 0.63 - 0.497 = 0.133
So we will get 10 more gpt from center city squares before Sanitation, and 15 gpt after. Not as much as Beorn said
, but it's nice economy boost. Also corruption will be 13.3% less. Sounds good, lets try India then 
Btw, Stock Exchanges increace tax output, like markets and banks, but not research
OCN on standart map is 20. Deity level cut it to 12 (or 15 if commercial).
Rank corruption for cities with rank = 1,2,...,5:
1 >> 0.042
2 >> 0.084
3 >> 0.126
4 >> 0.168
5 >> 0.210
With commercial trait:
1 >> 0.033
2 >> 0.066
3 >> 0.099
4 >> 0.133
5 >> 0.166
Corruption difference = 0.63 - 0.497 = 0.133
So we will get 10 more gpt from center city squares before Sanitation, and 15 gpt after. Not as much as Beorn said


Btw, Stock Exchanges increace tax output, like markets and banks, but not research
