What about with tariffs? Seems in that case its not relying on the taxation of citizens for income. (Could this lead to the gov being less obligated to be transparent about its income??)

The trouble with tariffs is that they make imported goods more expensive or the domestic population, rather than directly taxing foreign producers. A producer hell-bent on exporting to a country whose government imposes tariffs might lower his margin a little but there's only so much most producers can do. If you, say, operate with a 10% margin and a tariff of 25% is levied, your only options are to not export your goods or raise the price for them. In this example, either option causes a disadvantage for the domestic population, either by paying more of their money to their government (eeriely similar to a tax) or by having fewer options and having to go with another good which might be more expensive.