[Personal note to William and others who know I'm generally strongly against developing finance: THIS is what I'm interesting in for the direction of the game. Inward, not outward. Services are a fundamental subset of this industrial game that are currently neglected. "Finances", on the other hand, are an all-encompassing super-set that I'm afraid will make the existing game irrelevant.]
I had spent over 2 hours composing a post, which started brainstorming how to implement services. My computer crashed and I lost that post. Anyway... I expect to take at least 2 weeks to flesh out anything I would consider an adequate suggestion. But here the summary of what I had typed.
I call "media" firms "advertising", because that's all they do right now. Right now, newspapers don't need paper because they don't produce a paper product to sell to consumers, they only increase brand ratings. (I'll mention a sub-point that the theoretical product they supposed to produce is "news" and the advertising is a secondary service that just happens to be much more profitable

But is worth nothing that the I.P. rights of journalistic news is a current hot topic because of rampant Internet infringement. News is an "intangible good" that could be added to CapLab.) [I'll note that I am not a proponent of I.P., but it would be significant if CapLab could ever be used to test the merit of I.P. regulations. Well, I.P. is certainly a "capitalistic" idea

]
All advertising firms are services, as opposed to the more tangible goods which all consumer industries in the game produce. It seems that services will be added to the game once we flesh out how to do it. Thus,
considering how to correctly implement advertising firms should be taken as how to implement all services.
Before we add services, I think I want to add equipment (as more than it's current of being just some "line-item"). Supplies are a short-term monthly expense, and equipment is a long-term asset that incurs depreciation and maintenance. Since all our current industries are product of goods, they all have some significant equipment needs, and the fact that some industries equipment costs should notably lower than others is overlooked. This is more of a problem with services, because some services will need nearly 0 equipment, and the requirements for some services are almost 100% equipment. (Quick examples: Ground Shipping needs Trucks as equipment (not supplies); Radio arguably requires nothing more than labor and a broadcasting tower.) But, the including of equipment is another subject.
All services need equipment, supplies and labor. The supplies may or may not be goods already in the game, like "paper", if a "newspaper" product were ever to be sold to consumers.
Of course Internet advertising is missing from the game. But about the time you mention that, I might mention you should remove newspaper from the game. Newspaper's been depreciated, and we all currently get to watch the former industry giants deal with that fact

But I might mention I'm confused by what is supposed to be the Great Vision of how time passes in this game. CapLab introduced obsoletion of old products, yet they change the start date from 1920 to 1990? You just skipped over all the old products we want to phase out, lol. That's inconsistent to me, and that's possible a results of not following a single vision and having too many cooks in the kitchen. If we're supposed to be following history, a huge steel industry fell to fiberglass which fell to carbon fiber. But if your starting in 1990, okay, skip it, steel's not a giant. Compared to the significance of the fall of steel, the fact that Smartphones replaced Cellphones is nearly just a matter of semantics. They still often use cell towers as opposed exclusive wireless LAN connections. *shrug* Back on topic...
After advertising, the other significant and more transparent service industry already in the game is freight or shipping. We pay freight costs, and products are shipped overseas, but it's otherwise invisible.
So, we need to start looking at how to develop these two servers and prepare to offer new services.
The 9-square layout: Although I'm a fan of the whimsical nature of the 9-square layout, there is plenty of opposition too it. The primary point is probably "versatility". I currently feel the 9-square-layout either should be eliminated, or greatly enhanced, but the great enhancement may require as much work as the whole game has already required. Thus, it should be eliminated. But, that's something to look at later in the process of developing services.
To start the process of developing services, I just wanted to start brainstorming. Give a list of services, their required inputs, their requirements for production, and what effects they produce. And all of this is arguable. But, get a bucket list, see what's feasible to include, what elements should be excluded, and then we can consider implementations such as the 9-square layout. Such as is it okay for dry cleaners to require chemical minerals as supplies, or chemical minerals & soap? No matter yet: I'm working on the framework, not necessarily the (sub-) specifics.
My template right now is: Inputs + Processing + Outputs
Service Industry: [clients/products + supplies] + [equipment + labor] = [product + effect]
I need to refine the format.
I seem to notice I want to exclude a lot of the supply links, because there would be too many. This is a substantial difference from current goods-focused industries. Our belt shop can easily show where it gets leather from. Our Advertising firms can show a long list of it's clients... but for other industries that not only have firms as clientele, but also the general public, it makes the idea of "client list" (a list of people who supply the goods or opportunity for us to work) become vague, nonspecific, and maybe irrelevant.
Advertising is in Game. Newspaper is notable as whether or not to include not only paper, but also intangible good [IP] "news". Dang, just realize the business of Journalism is the reselling of news. Newspapers do (or did) the most news manufacturing, followed closely by television. However, radio stations are resellers, not creators of news. We also neglect the entertainment produced by almost all media firms (which helps explain why I currently call them advertising firms and not media firms).
- Newspaper: [paper + dyestuffs + clients] + [labor + printing press] = increase brand rating + entertainment + news + newspaper
Require paper & ink? Produce a physical product which could be sold at convenience stores, e.g.?
- Radio: [client + news] + [equipment + labor] = increase brand rating + entertainment + news
Already partially implemented. Notable as you only need a single piece of equipment to start a potentially significant business.
- Ground Shipping: freight + packing supplies + [labor + vehicles] = relocation of products
Shipping & Transportation! Now that's a big industry that does have a significant impact in the current game.
- Dry Cleaner: [apparel/leather goods + chemical minerals + detergent] + [equipment (steam-press, laundry) + labor] = apparel/leather goods
A simple example of "refining existing products".
- Landscaping: [clients + supplies] + [equipment + labor] = Increased property value.
Landscaping is interesting because the supplies and equipment it needs are mostly inexpensive and also highly variable. Will we require generic supplies for all industries? Or Will we exclude generic supplies? Or it depends?
- Waste Removal/Junk/Recyling:
Here's a big idea. I get mad that I can empty my entire inventory with the click of a button. It should cost a small fortune to get of that stuff. That's why people end up with warehouse full of junk, because it often costs more to dispose of obsolete products than it does to store them. Big industry, closely related to shipping as far as game mechanics, I imagine.
Of course there's lots more. I just had to get something posted. I'll start a new thread in two weeks, tentatively.
tldr;
Internet advertising should be included.
But, how to properly implement advertising firms, shipping, and all future service industries is whole 'nother can of worms
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EDIT: Last updated to include junk / recyling}