Solving the causes of these problems

Trucks take goods from generic industry or import it from the region, marked as pink in the outside connections overview, to commercial buildings which then sell these goods. If commercial buildings not get enough goods, they give the "Not enough goods to sell" warning. If commercial buildings don't get the goods in a fixed amount of time, after this warning they go out of business and abandon the building. How to fix this problem? Get the goods to the commercial buildings by trucks. From the a generic industry building, highway, train station or harbor. Problem solved, right? Usually not. Why?You make a cargo train station, hundreds of trucks keep spawning at it, you make a harbor, same thing happens, your highways are packed full of pink trucks bringing goods to your city. You traffic grinds to a halt, trucks start to despawn and commercial buildings don't get their goods. The problem just keeps getting worse. Why? Because you made a city that doesn't produce it's own goods. It is forced to import them. And that creates lots and lots of extra traffic. Or, you made a city that does produce goods, but in industry districts that are far removed from commercial buildings so you can prevent pollution from poisoning your citizens, in residential zones, that live close to your commercial zones. This just crates more problems with traffic and ends with "Not enough goods to sell". It's not that they aren't made, the goods, it's that they can't get to where they are needed.You first have to understand the industry production chain, which is actually problematic because the developers forgot, for years now, to add RAW items, to the overlay. You can see them in the ground, but not in the all important import / export overlay. Trucks carry raw ore, oil, wood etc. But the overplay shows just the PRODUCTS and GOODS. Not the RAW items. Confusing players who have product producing oil, forestry etc. industries in their cities. What you need to know is that buildings that extract ore, oil, cut down trees, also produce trucks, but those trucks are not separate, but fall under the products category of the overlay. But. these are not products that go into generic industry to be made into goods. They go into product specific specialized industry buildings to be made into products, because they are RAW items. Then those buildings send out trucks with actual products towards generic industry buildings that produce the actual goods, which are then sent out, from these generic industry buildings, in trucks, to commercial buildings.In cities that have this full chain, traffic happens inside the city, and inside the industry zones, with only the goods transported to commercial zones. Any RAW items, resources you may call them, that are missing are imported from the region by highway, train or boat but ultimately transported by trucks. Which creates addition traffic.Traffic, traffic, traffic. It always comes back to traffic. So how do you actually make a city that doesn't buckle under this traffic strain from trucks transporting Raw items, products and goods? You incorporate industry and commercial zones into your residential zones. Yes, there is sound pollution, yes, there is ground pollution, but you can mitigate both by offices, trees, and layered zoning.Only by building producers and users of goods, right next to each other, do you eliminate lengthy trucks rides of your goods. This reduces traffic volume, while making sure that commercial buildings are getting their goods on time. If you also produce oil, ore, forest etc. products locally you additionally reduce traffic coming in from the region and trains and the boats. And if you even have RAW items, resource, production/extraction locally, you reduce the traffic from trucks even more, clearing the streets and highways of massive numbers of trucks that take very long rides.To summarize, no industry means no goods produces locally. Importing creates traffic, high traffic slows everything down, making commercial buildings lack goods to sell, which makes them go out of business. Producing the whole chain locally, RAW>PRODUCT>GOODS reduces traffic. Setting up generic industry close to commercial buildings reduces travel time for trucks transporting goods, preventing commercial buildings from not having enough goods to sell.My other guides if you are interested: