6. An older designed behavior called the "bulk rate tax" _seems_ to be hitting some players, but my suspicion is that they're trading in commodities that have really low supply/demand and are confusing normal price "wobble" due to supply/demand numbers <30,000 with the "bulk rate tax". However, it's possible that ships with cargo capacity above 400 are being hit by something I and other commanders cannot personally observe. I trade in a 272-ton Python, and I know another commander who trades in a 368-ton Anaconda, and we've _never_ seen the behavior that some players have been reporting as a "bulk rate tax". As for the tax itself and what it is, it's _supposed_ to affect you only when you bring a large quantity of a single commodity to a station that wants very little of that commodity. Search the forums for more.
The bulk rate tax is easy to observe. I even noticed it in a T6.
Basically this:
arrive at a station with a significant ratio of the stations demand and you will get lower sell prices than if you arrive with an empty hold.
so deliver 200 t of a commodity with demand numbers over 100000 and you will see negligible effect.
but deliver 200 t where the demand is 10000 it is noticeable and if the demand is 1000 your profit is reduced dramatically.
This is why bulk trading is best done to high population systems where the demand numbers usually are high
If you want to trade with a station with low demand numbers it can pay to split the cargo capacity over several commodities each trip