Late in the game, my capital has some decent trade going on.  I have 33 trade routes, all naval, and the Money screen gives me the following information, which all looks correct:

• Base of 33 Trade Routes (+1 money each) = 33 money from trade routes
• Customs Farm Infrastructure (+1 money generated from on-going Trade") = +33 money on trade routes
• Mandate Patronage religious tenet (+2 money per number of trade routes on City or Outpost) = +66, which seems to be added "from number of trade routes".  I'm happy with that.

Total that all up, and we have 132 money per turn.  Good so far!

The Great Fishmarket, unlike the Customs Farm, is grouped under infrastructure, so instead of increasing money on trade routes, it's a simple "+165 money from Great Fishmarket".  This math is correct (5x33 naval trade routes), but it's odd to see some things treated as "on-going Trade" and some being off to the side.

Finally, I'm going to build the Customs Agency infrastructure, which grants +10% Money generated from on-going Trade".   Let's see what it's going to give us!  10% of "132 from on-going Trade" (which is +13 money), or 10% of the 297 money we get from our trade routes and from the Great Fishmarket?  10% of that is only 30 money, which isn't huge, but the Seafood Wholesalers are on the way, which would add even more money per trade route.  Let's see what we get...

+7 Money per turn.  7 Money per turn from almost 3000 production is a bad investment, but right now I'm just really curious, "Why 7?"  At this point I'm pretty sure that it's only giving me 10% of the money coming from my Base Trade Routes (33) and the Customs Farm (33), so 10% of 66 is 6.6 ~= 7.  It's not factoring in my Great Fishmarket, and it's not even factoring in my Mandate Patronage Tenet which is directly improving money-on-trade.  I haven't done the math on the Venetians, so I don't know if their LT bonus on trade would be included in this 10% multiplier or not.  I'm guessing they aren't because their ability is worded the way the Great Fishmarket is worded instead of the way the Customs Farm is worded.

By the way, the Empire State Building cultural wonder gives "+20% Money generated from on-going Trade on all cities".  If that's calculated the same way the Customs Agency is, that would give my capital 14 extra money per turn.  I've never built the Empire State Building, but I didn't know it would be this bad.

Conclusion: Anything that increases your money from trade routes by a percentage is bad.  Anything that increases your money from trade routes by an integer per route is much better, and can be quite powerful mid-game.  I love the Great Fishmarket.

Bonus Proposal/[Idea]:  Increase the percentages on trade, and/or to include more factors

• Percentage bonuses on trade could/should include anything and everything that increases "money generated from on-going Trade", including Legacy Traits, Religious Tenets, and maybe even the Great Fishmarket and Seafood Wholesalers
• Percentage bonuses on trade can safely be increased to "+50% or +100% Money generated from on-going Trade" on all cities for the Customs Farm, and "+100% or +200% Money generated form on-Going Trade on All Cities" for the Empire State Building.  The Taj Mahal gives us a whopping 50% on all money on all cities!  The Empire State Building can at least make trade worthwhile.

Thank you for listening this far.  Santé!

Huh, I never noticed this. The reason for this can be seen in the properties of each bonus.

These are the Customs Farm and Customs Agency, respectively. They both directly modify the property MoneyGainPerTradeRoad which explains why they synergize with each other as intended.

This is the religion bonus. It doesn't actually modify the property MoneyGainPerTradeRoad, it just reads the number of trade roads and spits out its own value. Because it's not tied to the property, the game has no way of tracking this bonus and identifying it as a trade modifier. Luckily this could be easily changed without modifying assemblies by mirroring the effect of the Customs Farm.

Here are the Venetians. You're right, they wouldn't gain anything either since the bonus works the same way as the tenet. Unfortunately this one can't be fixed as easily. While the settlement has readable properties for TradeRoadCount  and NavalTradeRoadsCount, it doesn't actually have a writeable property for MoneyGainedPerNavalTradeRoad so there s no way to make ongoing trade benefit specifically from naval trade (same issue w/ Great Fishmarket). Still wouldn't be too hard to fix in the assembly but they'd need to conscript a programmer instead of just a gameplay designer.

Hi, thanks a lot for pointing this out. We filed a ticket for it.