Here is a quick alternative to the usual "the King takes 10%" approach to taxing the PCs. Something I'm generally opposed to, anyway, as adding limited reality for concrete annoyance.
The idea, basically, is like tax farming. Instead of the government exploiting a population via taxes, they sell the right to collect taxes to private concerns. The government gets its cash up front, the private concerns get what they can.
The Romans did a lot of this with mines, for example, and it's how paying up the chain worked in at least one episode of The Sopranos, too - not a percentage a week, but a flat rate to the guy above you. You come by that money however you need to - but you owe a specific amount.
It's a potentially amusing way to explain why dungeons full of loot are left to private adventurers and aren't just surrounded by the army and systematically leveled like The Black Company and friends did to the Barrowland (a classic 15-minute workday approach, actually, but I digress.)
You pay X, and get the right to exploit a given area.
It would explain the utter hostility of adventurers to each other in the dungeons.
It'll explain NPC tax collecting types.
It'll explain why you are adventurers, but those guys in room 2-14 are bandits - you paid, they're claim jumping.
It would also work well enough for groups splitting treasure - you buy in to the concern, and then take out your share. You've already paid what the government gets, and the rest is yours. And it matters not a whit to The King or the Lord Mayor or the local Shah if you die in a pit on level 2, because your profits are of no concern.
Charging a relatively large fee for exclusive rights would make sense if the government can enforce that (the army is around, say, or there are legal punishments to claim-jumping). Charging a relatively small fee for non-exclusive exploitation rights makes sense if the rate of return is somewhat low (lots of dead, a few rich types) or if they can't enforce the rules. Or have an excess population to bleed off. It's an approach that makes more sense in a settled world (lots of people, too many unemployed youths in the cities and countryside and not enough fund to draft them) and less so in a "points of light" game.
It might be a fun explanation of why the PCs get to keep their whole take, and why "strip it of everything I can take" is such an important strategy.
Oh, and you can make it a yearly thing - pay and exploit, or don't and don't. You'd probably see a lot of expeditions rarin' to go during the Spring start of the looting year, and some desperate types in late Winter trying to get in the last trips they can afford and finally hit paydirt . . .