I was reading few days ago about an interesting case regarding these taxes. It happens in the Ottoman Empire where the muslims give soldiers while the non-Muslims pay taxes.
The year is 1898 and villagers from today's Northern Greece (which is still in the Ottoman Empire in 1898) run away to Bulgaria (which is free at the time). When they realized that they have to go to the Bulgarian army they all come back to their village in northern greece, willing to pay the taxes
But there were many things that were irritating the non-muslims. Apart from being treated as a low class, their taxes (this tax is called desetok in slavic, which is 10% of the income) could have been bought from the state by an individual who then had the right to collect the taxes (i don't know the english term for this).
For example, the village Juventuz has to pay the state 10% of this year's income which is 10 000 eur. The state sells the tax to an individual from the Milan forums for 10 000 eur and this individual can now ask for as much as he wants. At the end, the guy collects 30 000 eur from Juventuz, or 30% of the income. It goes up year by year and there are cases when almost 90% went for taxes. The state got its money and they don't need to go to the village to collect the money. It's up to the guy who paid the money to the state to collect the money from the village, in whatever way he wants.
And only the taxes of the non-muslims could have been sold to individuals.