Commerce Seems Flawed
I feel as though the game has serious issues with commerce. Without spamming trading posts I cannot generate enough cash. I put specialists in all of my commerce related buildings, reduced my army, deleted/sold any "old" buildings and still could not generate very much cash.
I have noticed this seems to do with harbors as I have read in other posts. My civ with about 10 cities was generating good cash until I started building harbors. They (eventually) caused all my trade routes to break. This issue has been discussed I realize but I would like to point out that in my case, once I sold every harbor I owned my trade routes were restored but NOT my revenues. The Trade Route overlay confirmed my routes were re-established but I never recovered the revenue.
The whole commerce issues are what is killing this game for me. I never had these challenges with any other civ game. It feels totally buggy and is my number one issue with this game. I have had thus problem in each civ 5 game I have played thus far. Until it is fixed I just don't feel like playing because (eventually) all my effort in the early game ensuring I have a good economy are all for nothing by the middle of the game when the commerce just goes off the rails. Sad.
This is just one of the (many) bugs that are currently wrecking the enjoyment of this game. Only thing you can do is wait. If Civ IV was any indication, the stability issues and major bugs and balance issues will all be fixed ... in the first paid expansion.
Be prepared to shell out another $40 on top of whatever you already paid.
I once had a game when each turn generated +122gold.
From what I recall, it was towards the end of the game on settler mode, epic time, and some years after several negative-gaining turns (ie -12gold/turn...during wars/conquering).
Further, my stash was in excess of 30,000 gold. I wish I had made notes about what I did to generate so much. With other games I played thereafter, I have not been able to generate as much, but that doesn't mean it wouldn't be possible again.
I usually do not have issues with maintenance.
1) One thing I find that helps is to hover your cursor over the build list on the city screen. It tells you how much that city spends per turn on maintenance. Then compare that to how much it brings in. If it is loosing money. build more trade posts. If it is positive, build more farms/mines ect
2) I usually do not settle a city unless the location has:
a.A river(+1 gold)
b.2-3 luxury resources(not necessarily new ones)
Hope that helps
P.S. - Making merchant specialists is a big mistake unless your happiness is capped. Put those citizens on grassland trade posts(+2 gold and +2 food) so that the city can grow and you can work more trade posts.
P.P.S - If you post some pics of your city screens, or even a save file we could probably help some more.
As I said the major issue for me is the need to spam trading posts and equally the bug with trade routes and/or harbours. Please, devs, make note to address this.
You could be running out of gold for any number of reasons. If you want the problem addressed specifically we need more details.
In general if you are running low on gold, you can delete a couple units/workers if you have extra, you can look at your road system and see if any are useless and just costing you money. You should build a market and bank in your capitol and in a city that has lots of gold. Maybe you built too many useless buildings and the maintenance from them is what is hurting you. Are you working all your fish tiles in coastal city with a work boat? Etc.
Once you've done a basic check of these above issues, if you are still losing money the answer is simple.
Build more cities. Every one you plant will give you gold. On quick speed prince i believe it to be around 5 gold or more per turn you'll gain. Try to plant near fish so you can buy a workboat the same turn you build the city, You'll gain gold for planting it then the next turn gain 2 or 3 more for the fish. If you are losing gold sacrifice happiness a bit by spamming settlers and planting in intelligent places.
^Generally good advice but one thing I would add is to avoid buying items outright if you can help it. Buying items is usually ~5x the opportunity cost of building them with hammers. Save that money for dealing with city-states/other civs/emergencies IMO.
To the OP, I have not encountered the the bug you are talking about about though I do not doubt it. How much does it say your returns are from trade routes on the commerce tooltip?
Cash flow comes down simply to tiles worked.
Maintenance and unit cost obviously fights you.
Now with civics you have two main routes. ICS or large concentrated cities.
I have found myself in the rennaisance era with 280 gold per turn on standard map, emperor as China. The key factor for me was ICS, papermills, and river tiles.
I would pay off maritime CS's for growth, build happiness in all cities, and focus on economic and production buildings. At my best I had around 8 cities, 12-16 population per city, 250 gold per turn, and about 13 happiness.
At my worst, I had 29 cities, 9 pop average, 45 gold per turn, and 51 happiness...once I got the maritime cs's liberated again and pop went back up, I was back in the 200+ gold per turn.
I hope that they fix the harbor problem with the next patch.
In my second game, I had 10 000 (ten thousand) gold coins. Once Lizzy knocked on my door all that money went out the door buying troops to fend her off.
In my other 5 games, I had problems making money, and I wonder how the heck I did that. So there is a trick to it, I just don't know how it's done, but it can be done.
I agree that spamming trading posts is the only way to keep your civilization moving forward. I've tried playing a more conservative route (a few trading posts, farms on river tiles and wheat, etc) but I've found I run short of gold. Especially, when you are called on to defend against an attack.
I'm not sure about the harbor issue as I've only built them a few times and didn't notice anything obvious.
Hopefully, commerce issues can be tweaked to make the other tile improvements more attractive or make trading posts less needed.
Trading post spam on river basins seems counter intuitive( since this is traditionally where farms go), but it's the best in terms of money. You honestly don't need any farms as magical maritime food, base food bonuses, and MAYBE a granary in a city you want to grow keep your cities in the green.
I agree that money making needs to be more varied ( like selling services not just gold).
Side note: Unit maintenance, I am often surprised to find, increases both with worker and with troops. So often I forget this fact that when I conquer and have a flock of captured workers I forget to disband them and suffer the consequences.