I've yet to see any planet that creates firearms.
Firearms are created by heavy industrial conditions and are quickly delivered from free market to military bases and low-stability worlds as well as being smuggled to pirates. Not seeing them in surplus means that there are too many low-stability worlds in the local area. I`ll tweak the numbers though.
I've seen basically a billion weapons created by the Marauders Scavengers upon finishing their scavenging operation. I feel like their cargo should be limited to metals, rare metals, ship parts, weapon parts, electronics, and heavy machinery, rather than hand weapons, luxury goods, and recreational drugs. They are scavengers, and it doesn't make sense that they are the largest producers of firearms/luxury goods in the sector with their salvage operations.
There's usually a fair number of weapons owned by each military base that you can pick up if you have enough rep. But they don't replenish quickly.
Psy Clones/Rock Blasts are practically nonexistent in market.
Blasts are produced at specific locations at very limited amounts, so these never will be available for sale at any world except for those that have met their drug demands (psy clones/recreational/blasts) and the FFS rock fly farm.
Clones are exclusively UIN-produced drug replacements that are universally accepted (illegal in RSF though). They are available at UIN electronic facilities. [/quote]
I don't think I've ever seen a good way to make a profit on Psy Clones, the cheapest ones are as far as I know, located on Freya in Centronom, and still the cost is ~450-550, selling for at most 600. After tariffs, the profit is close to 0, if any exists.
Blast drugs are always worth picking up at the Rock Farm if you don't care about your rep with a faction, or if you want to move it to a pirate base/marauders/black widows.
Medicaments, Luxury Goods, Domestic Goods, Volatiles, and Food markets aren't worth trading at all; practically no profit margin exists.
Meds, luxury, organs and domestics are demanded mostly by well developed and/or high stability worlds. Try selling these to markets with stability >= 5.
Drugs, hand weapons, food and supplies are demanded by low stability worlds.
Dropping stability of a large-size world below 4 will increase demands of the second group of commodities while almost entirely dropping demands of the first one. Increasing stability to higher than/equal to 5 will switch demands in the opposite way. Actual stability plays a role in demand formula in both cases, so a world with 1 stability is the best place for a smuggler while the other one is for merchants.
The profit margin after tariffs on most of these is quite low, if any, with the exception of Luxury Goods. You can usually pick them up on places like the FFS for ~900-1000 per unit, and sell them to a high stability world for ~1600. Volatiles can be used to make a profit, but without abusing the save bug where saves do not remember how flooded the market was to adjust prices, markets get flooded on Volatiles when you have ~3000 units you are trying to sell for a profit. If you do want to abuse the save bug, there are better goods for it.
Food can be sold to the Marauder Hideout for a profit.
I never find enough domestic goods to make any decent volume of trading happen.
The biggest abuse I can see involves the save bug. Simply purchase as much rare metal as possible at ~600 or less, have it in a high stability world that does not sell rare metals (Danbridge in Shington, or Vella in Gianopolis are perfect). Sell ~200 units of it at the planet, it sells for ~1400 per unit. Save and exit the game. Reload, sell another 200 at 1400, save and exit, reload, repeat. Rare metals are insanely good for trading at these planets anyways (600->1400 without any shortages, with planets that sell Rare Metals within the system for each. (Even without the bug, it can be used to quickly make ~100k from nothing). I need to test to see if the save bug is an Ironclads only thing, or whether it should be reported as an actual bug. It's less of an issue in the base game, since the base game has ~30% tariffs everywhere.
I'll need to experiment with crashing economies at a later date (flood black market with goods, crashing stability and the prices of all the goods on the market, buy those up, can it make a profit?)
The biggest profit I've made so far was from Jorgia to the trading hub, when the trading hub had a shortage and hit 110 on ores. Turned all of Jorgia's ore over to the hub, netting me ~7 million credits.