You've got global settings that apply to all ships and or stations. Essentially you're creating new global defaults that apply to everything you own/operate. The two check boxes at the top of the new trade rule screen, Station Trades and Station Supply, will apply that to all your property. If you want to create trade rules that only apply to certain stations or certain ships, you do NOT want to check those boxes.
Now, lets say you've created your trade rule, and it is not applied to everything. A basic trade rule like "Only My Faction"... where you hit the checkbox to restrict all factions, the section that used to say additionally restricted factions now changed to Allowed Factions, you select only your own faction.
There are multiple places you can enact this trade rule. On a ship or station, in their info screen, the last tab is Individual Instructions... you can choose to apply that trade rule to that specific trader, or to a station which will effect all the traders of that station. You can apply it only to a ship, so only that ship will use that trade rule. You can also apply that trade rule to a specific ware, and specifically to the buy OR sell, or both... of that ware. And you can do that for each ware in the station if you want.
For an example, I have 3 basic trade rules I use in every game:
- Only Me, so only my faction can trade.
- Only NOT Me, so everyone but me can trade, and
- Absolutely No One... so no one can trade.
Now we'll take a station that produces say Hull Parts, and its completely self sufficient - it produces its own ECells. I don't want my traders selling ECells, because I want them selling Hull Parts. I also don't want anyone selling me ECells because I produce more than I need... but I don't care if NPC's come and buy ECells from me. So under ECells, under buy, I use the Absolutely No One trade rule so no one, not even my own faction or that station's own traders, will try to buy ECells... because I already produce what I need. Then under the sell option, I use the Anyone But Me trade rule... so that way my own traders won't actively try to sell ECells... but other factions can come and purchase ECells if they want to.... but I'm not wasting my own traders time. I'll use those 2 trade rules in the vast majority of my stations for the vast majority of tiered wares. We'll take that Hull Parts complex again, a very basic one with no workforce. To make hull parts you need refined metals, ecells, and graphene. I only want my traders selling Hull Parts... but I don't care if the NPC's come to buy my excess ECells, refined metals, or graphene. So I'll apply those 2 trade rules to every product in the chain that isn't Hull Parts... that way my traders can ONLY try and sell Hull Parts, but NPCs can come and buy graphene, refined metals, or ECells when I have a large stock and the price is right for them. The NPC's are doing the legwork for stuff I don't care about.... and my traders are sticking to the profitable final products.
Say you are a fan of HoP and don't like PAR, and you have auto miners and auto traders working in the HoP areas, but you also catch them buying and selling to PAR. You could create a trade rule that restricts business with only the PAR faction... and then apply that to any stations or ships you have in that area.... so they'll just ignore any and all trade offers/ware needs from just that one faction, while allowing you to do business with the rest of them.
~ u/grapedog on Reddit