It appears to depend on the initial quantity that the player brings into the dockscreen.
E.g. corporate enclave and titanium ore:
Start with 20 tons, sell them, get another 20 tons -> Corporate enclave not interested in buying any more.
Start with 50 tons, sell them one at a time -> Corporate enclave buys up to 25 tons, price for each dropping as inventory increases. Alternatively, sell them all at once to bypass sell limit and receive full price.
There are several bugs and balance issues with this phenomena, i.e. the gameplay effect this has on ships with limited cargospace.
As I posted here: https://forums.kronosaur.com/viewtopic.php?f=2&t=6405&start=15#p57194
"[I think station buy limits] should be reworked to be less obtuse and exploity. Probably the limits should be raised, and stations should only offer to buy the difference between what they have and the limit. You'd have to find a way to set limits that maintains game balance. As a starting point, you could use some number of tons worth, some amount of money worth, or some number of items, whichever is lowest. The values could also be multiplied by some factor representing the size of the station's economy, like money generation rate."
Also, this reminded me of another issue with selling items to stations: http://ministry.kronosaur.com/record.hexm?id=1365
I’m not wholly sure I agree that this behavior needs changed. I even have my own headcanon for how the current version works:
Player: What’s your rate for buying plasteel ore?
Station: Plasteel? Eh, let’s say… 68cr per ton.
Player: Groovy! I’ve got two hundred tons of the stuff.
Station: …Kack. >.<
The various stations already screw the player over fairly righteously in the name of trying to make a buck — charging a lot more than they’ll give for anything unidentified, even above the usual markup, just to name one example. Giving the player a way to put the screws to the stations in return is… somewhat gratifying.
I'm not sure what the fix is, but I'm not 100% happy with the current system either. Any mechanic which tempts the player into getting an advantage via mindless/boring activities seems wrong to me.
Ideally there would be some way for the player to get an advantage in a non-boring way, but I don't know what that is yet.
We already have trade convoys moving stuff between stations to a limited extent (I think black market convoys actually move goods sometimes but I could be wrong). Maybe when the system is generated, the engine could look at what "source stations" like mines and "sink stations" like corporate stations are present. Then a certain number of trade routes could be mapped and a freighter assigned and generated to each trade route, ordered to move between two stations picking up a commodity produced by one and depositing it at the other.
The source station would slowly and continuously generate the commodity and put most of it in the freighter when it arrives, and the hidden stockpile of the commodity at the sink station would continuously dwindle (this already happens). Thus, the sink station would pay less for the commodity immediately after the freighter arrives and pay the most for it immediately before it arrives, when supplies are lowest.
If the freighter is late or mysteriously destroyed, or it doesn't bring enough of the commodity (because the player sneakily bought up the entire supply right before the convoy arrived at the supply station), the player will be able to sell the commodity at an inflated price. If the trade route is unprofitable for the freighter enough times or is too risky (freighter gets attacked by hostile ships a couple of times, even if it survives), the freighter will gate out and the player can exploit the trade route for a little while until a faster and more heavily armed freighter gates in.
If the engine determines that the trade route was disrupted by player actions (direct, witnessed attacks on Commonwealth freighter types already trigger commonwealth justice, so I'm talking about unwitnessed attacks or players buying out the source station/ saturating the sink station leading to unprofitable runs), after a certain period of time Molotoks or other mercenary ships might gate in to administer a Teamsters-style lesson in business ethics. They wouldn't even necessarily have to go after the player directly, just circle the sink station and attack the player whenever they approach to encourage them to seek their fortunes somewhere else.
I suggest we take this to the forum: https://forums.kronosaur.com/viewtopic.php?f=3&t=7106
Fixed in 1.8 Alpha 4.