If one successfully builds the Trade Clearing Bureau, a tax can be set on marketplace transactions. Is there any reason not to immediately set the tax rate to the maximum of 25%? Perhaps the AI players are less inclined to buy and sell on the marketplace with a higher tax rate, but that's difficult to observe from the player perspective. Any insight would be most welcome!

Just if you feel like a generous god.

one negative could be (have not tested it):

the transaction tax is added to your income increasing dust "production" (that is where i am not sure), which increases inflation.

I think it also increases overall inflation, which makes dust related actions more expensive, but I wouldnt count that as a con for the player building the Bureau, since you get more dust anyway.

I also wonder about this. In my multiplayer game my ally set the tax to 25% with no fanfare - it seems somewhat silly to have it start at 10% in that case. Additionally, unless there's some hidden nuance to inflation, it almost never bothers the wealthiest person in the galaxy. I suppose inflation isn't good for your allies who aren't as wealthy, but that's hardly a significant issue.