Like the title says, change the main taxable event from trade to manufacturing.
Something that doesn’t produce any value like the mere exchange of existing goods shouldn’t be the main taxable event. Tax should occur when value is added, which is during production. Manufacturing fees are currently a joke, ship destruction is currently even an ISK faucet instead of a sink.
Increase the ISK cost of manufacturing so the ridiculous broker/sales fees can be lowered. It will lead to a more balanced system of isk sinks and faucets where destruction is actually removing ISK from the game and where trade isn’t artificially punished.
For actual implementation increase manufacturing fees so manufacturing becomes a sink of around 10b isk. Increase the effect of transaction tax reducing skills so it doesn’t look like you are backpedaling on the fee changes and to dissuade alpha bots.