Would you guys like some help with "real" world business? In my experience from starting and running my own company for 10 years...?
First off, high margin profits are not just for illegal/shady goods.
For example, jeans are bought whole sale for about $3. You buy them for $20 to $30 each. Thats up to a 1000% mark up on a perfectly legal trade good. Before costs.
There are THOUSANDS of similar mark ups in this world.
Take software for example.
Lets start with games. Games cost less than $10 per unit. This takes into account the making of the game as well as manufacturing it onto a disc or two. This is about what companies like Microsoft get per game disc. You see them retail for $50 to $70 at your local gaming store. That is a 5 to 700% mark up.
However, you need to be aware of the "typical chain". You have the manufacturer, who is likely also the "wholesaler", then you have a distributor, who buys from the wholesaler, and then sells to either another distributor who handles another region, or to retailers in their region. Then you have the retailer, who is typically the person a consumer buys from.
Each level of this tier system takes a cut, rule of thumb is 30% of final retail for each level of the tier.
Not all business' follow this, but a lot of them do.
So on average, a typical business should be making about 30% on every transaction that they do. This is before costs.
However, not all business' are "typical". Now a days fewer and fewer of them are following this "typical" model. More and more are going for higher profit margins, which is why you see costs jumping.
Also realize when you see a 10 cent increase in fuel your going to see an overall 30 cent increase in the retail prices you pay.
Now obviously this isn't a cost jump you will see in each and every item.
A candy bar is not going to jump 30 cents in price, simply because people will likely stop buying them if they are seen/perceived as too expensive. So the candy bar will go up maybe 5 cents. This is because candy bars are bought by the box by retailers. So that 30 cents was an increase for the box of candy bars, not for each candy bar, so the cost increase is spread out over however many candy bars are in that box.
So the bottom line of what I am telling you is that you may think a 400% profit margin on trading is so good it has to be illegal, but it isn't. It is entirely possible to find these kinds of deals on a regular basis.
This breaks down for Traveller for one simple reason.
The Trade system in Traveller is set up to be simple enough for people to actually use it.
So we are trading off realism to get ease of play.
Some people already say the Trade system in Traveller is complex. Now imagine what it would have to be like to be as realistic as possible for millions of situations.
So I suggest the system just be accepted as is, as simple as it is, because if you want realism the rule book on trade alone would become a manual. A manual hundreds, if not thousands, of pages thick. For each planet.
So just accept for being as simple as it is, it actually works pretty darn well.