the one with 30.2 is from AI, the limit for players is 30

still a valid question why is there a limit at 30?

Players can set up to 60 for Rare Materials, but only up to 30 for all other resources. AI can set everything up to 60.
Reason is (was), that players cannot "run down" AI's economic via market ..

Can you elaborate on the reason not sure I understand

The AI in this game is very stupid and simple, even Elite-AI ..
.. and because the AI is not able to think, she needs an advantage to be reasonably competitive ..


.. also, for example, the AI knows everytime, even without espionage, where the enemy has which troops ..

Pardon my ignorance but how can you ruin AI nation's economy via market? Lets say there was no maximum value for resources to be traded how does that give me an advantage over AI?

AI does not conduct expansion wars but defensive wars and does not conduct any direct trade, so it has to compensate for its increasing demand for resources (for construction / units..) during the game by selling surpluses and buying missing res -- whereas players can also conquer new provinces and thus resources ..

.. so should, for example, one or more players try to monopolize the trade through permanent highest bids, the AI can outbid this (at the important resources which are necessary for buildings and unit production AI can compete each other at a higher price level) ..

.. or if maybe already early in the game most or all players want to buy the same rare res (..e.g. wares on the 25p map..) the price will rise quickly and a lot of buy offers with highest price will placed soon -- but if then an AI needs this res it would have no chance to buy it for a long time if she can only offer the same maximum price as the players, but actual it can always offer the highest price and get the trade as soon as the res will offered ..

Also a trained group of users who understands how the market works can just make it suitable for them, removing the chance for the rest to use it properly.

If the mechanic is the same as in their oldest game and I think it is, each player has different values in the market that comes from the AI.