If another station in the system has a better price than the current station, then the Trade Computer offers that price, even if other systems offer a better price. When docked at the station offering the best price in the system, the Trade Computer talks about better offers in other system.
At minimum we should explain this to the player (somehow). Or we can show both prices (best in-system price and best out of system price).
In addition, perhaps there is a way to show the price in all known systems.
So rpgItemTradeComputer returns a struct containing 9 items, but in 2 out of 3 places it's used, only 'sellRecommendation is used. In dsRPGCommoditiesExchangeSell, some of the others are used to determine which recommendation string to use.
For simplicity, I'd suggest instead optionally passing an object into the function and having the function return a single recommendation string that suggests the best nearby system (if the price is better there than anywhere in the current system) and a station in the current system (if the price is better than at the specified object).
If there's a planned use for the other data in the return struct or mods that rely on it, we could instead add additional versions of the recommendation string to it while keeping the existing data, and maybe use a new helper function to get just a single recommendation string.
At the moment the trade computer offers nothing on damaged items that can be sold. However there are stations that buy damaged goods like:
Armor dealers, Weapons dealers and Tinkers. Usually Tinkers offer best pricing and will buy anything that is damaged.
Illegal goods: They are partly handled by the trade computer, it will only refer to black market stations, but best price for most of these are from Startons (Victoria's nightclub) and also Corporate enclaves buy these.
I've noticed that the trade computer does also recommend to sell items in a certain system even if the station in that system buying these items has been destroyed ,for example illegal items in Rigel, after having destroyed the black market there and having moved on to the next system.
The trade computer does not take buying limits in account, it will happily sent you to a station that offered best price, but does not buy any more because its limits have been reached.
Excluding damaged items appears to be deliberate, though I don't see the point.
Startons and enclaves buy illegals in nonstandard ways, which probably is why they aren't included. The issue with the destroyed station means sysGetItemBuyPrice either fails to exclude destroyed stations or knows illegals can be sold to enclaves, even though objGetBuyPrice doesn't.
Buy limits would be hard to take into account, especially for systems other than the current one, since objects in those systems aren't loaded.
For info, the trading computer can also cause lag in the three screens that use it. Only happens if about 100 nodes are known. I'll open a ticket with more info soon.
Merged into 1.8 Beta 3. Thanks!