A 60% tax is pretty freaking brutal. Prices are already so similar most of the time that it's not really going to change anything to have a lower tariff.

Yes, a 60% tax is fairly brutal. Good thing we don't actually have a 60% tax most of the time in the game, then, isn't it?

A 30% tax adding to the purchase cost Y and a 30% tax reducing the sale price X*Y results in a tax which is always equal to 30% of the value of the goods traded, or equal to up to 30% of the total number of credits which change hands. Relative to the value of the goods, the fraction taken as tax is (0.3 + 0.3*X)*Y/((1 + X)*Y) = (0.3 + 0.3*X)/(1 + X) = 0.3; the fraction relative to the total number of credits which change hands is (0.3 + 0.3*X)*Y/((1.3 + X)*Y) = 0.3*(1 + X)/(1.3 + X), which approaches 0.3 from below as X goes to infinity. If we instead compare just to the sale value, then the fraction taken as taxes is 0.3*(1 + X)*Y/(X*Y) = 0.3*(1 + X)/X, which goes to 30% from above as X goes to infinity, and only reaches 60% when you sell for the same price as you buy; if selling at twice the purchase price, the fraction taken in tariffs is 45% of the total value of the sale.

If you would like to determine how much of the nominal net profit the taxes cost you (i.e. the difference between the listed purchase and sale prices), then you would like to use the fraction (0.3 + 0.3*X)*Y/(X*Y - Y) = 0.3*(1 + X)/(X - 1), which goes to 0.3 from above as X goes to infinity, and which goes to infinity as X approaches 1. For values of X greater than 3, this fraction is less than 0.6, while for values of X less than about 1.857, this fraction is greater than 1 (i.e. it is not possible to turn a profit if the sale price is less than 1.857 times the purchase value). For X = 8 (approximately what you'd see trading food from Eos to a world with a shortage), this fraction is about 0.386 (i.e. tariffs eat about 39% of your potential profit), while for X = 2 this fraction is about 90% of the nominal profit. This is a somewhat odd way to compute the tax rate, however, as the tax is on the value of the transaction and not on your nominal profit.

If you would instead like to compare the fraction taken as taxes to the net profit after tax but before shipping costs, then the fraction becomes 0.3*(1 + X)*Y/((0.7*X - 0.3)*Y) = 0.3*(1 + X)/(0.7*X - 0.3), which goes to 3/7 from above as X goes to infinity and goes to infinity as X approaches 3/7 from above. This fraction reaches 0.6 when X = 4, though it must be remembered that this is relative to the profit

after tax; the fraction gets lower as X goes to infinity and higher as X goes to zero. This method of evaluating the tax rate is merely a curiosity and is not a useful measure.

Because the tax is on the value of the goods and not on the profit, the latter two methods of evaluating the tax rate are at best questionable and are highly dependent on the value of X. The first two methods are more appropriate for evaluating the tax rate and result in either a flat 30% tax rate (relative to the value of the goods) or a tax rate relative to the total transaction bounded between ~23% (X = 0) and 30% (X goes to infinity). The fourth method can be useful for evaluating how much of your potential profit is lost to the tariffs and for determining whether or not it's worth making a trade run for a given commodity, but is otherwise not useful for evaluating the tax rate. The fifth and final method is merely a curiosity and worthless as a practical means to evaluate the tax rate.

One additional measure would be the tariff relative to the purchase cost of the goods, which would be equal to (0.3 + 0.3*X)*100%, where X is the ratio between the sale and purchase price (i.e. if you purchase goods for Y credits per unit, you sell goods at X*Y credits per unit). This measure, as with the fifth measure given previously, is more a curiosity than a useful measure of the tariff. It is nevertheless a useful tool for creating hyperbolic statements about the magnitude of the tariff. For example, if you're selling for 8 times the purchase costs of the goods, the tariff by this measure is 270%. Just don't mention that it's 270% of the cost of purchasing the goods and only about 34% of the value you sold the goods for.

A 60% tax is pretty freaking brutal. Prices are already so similar most of the time that it's not really going to change anything to have a lower tariff.

If it would not change anything, why would you want it?

If you drop the lower tariff, trading becomes profitable (before accounting for shipping costs) at about 1.429 times the purchase cost of the goods, as opposed to becoming profitable at roughly 1.857 times the purchase cost, which means it would be considerably easier to make regular trade runs while not running at a loss, though this seems to run counter to Alex's intentions for the game. I think that the "it's not really going to change anything" is more with regards to the current prices of commodities than to anything else, as buying goods at 20 credits and selling them at 40 currently gives a net profit before shipping expenses of 2 credits per unit; with the removal of the export tariff, that would jump to 8 credits per unit, which is considerably better but still small change by comparison to trading food at shortage prices (buying food at 50 credits per unit and selling at 200 credits per unit gives a net profit before shipping expenses of 75 credits per unit on the open market, and those are not exactly the best prices I've ever seen for food; if the export tariff is dropped in this scenario, the net profit before shipping expenses becomes 90 credits per unit).

On the topic of trade, smuggling seems to be nearly impossible in the long run. My first play through of the update I was running drugs and other illegal goods under the nose of the Sindrian Diktat until my rep was low enough for the black market to not trade with me. Afterward I tried to find another faction that would tolerate my trading with no luck. I don't understand why the black market would shut out one of their biggest suppliers because their government doesn't like me.

The Black Market might not shut you out, but the docking authority would, assuming that the docking authority is relatively clean.