Adventurers have a curious role in society. They are seen as both slightly scandalous and glamorous, and inevitably attract great curiosity among all classes of society, from the lumpen all the way to patricians. What distinguishes them from common mercenaries and other such base and less glamorous professions is that they, at least in theory, do not work for money. This means that at least the leader, and hopefully several others of his group (except for those which work as his retainers) must not be seen as doing something for profit. However, adventurers are also expected to be generous with their money (which is part of the reason their more scandalous behaviors are tolerated). So the question is: How do they support themselves, given their huge expenditures?
The easiest solution is, of course, to be independently wealthy - usually by inheriting that wealth, but occasionally through a previous career. If this is not possible, then grand "expeditions" to other regions are a popular way of fund-raising. What would be seen as gross theft, grave-robbing, and worse if perpetrated within the Flannish Cities is seen as thrilling derring-do when it happens a thousand or more miles away at home, and is sure to be reported on excitedly by the press and high society. Such plundered items will be displayed prominently in the adventurer's home - and if some of the items are discreetly auctioned off, so what of it?
Another possibility is to publish stories of one's adventures (and if these are not written by the adventurer himself but some hired writer, so what of it?). Such lurid and often exaggerated tales of one's deeds are printed in massive numbers on cheap papers, and remain popular with members of all classes capable of reading who dream of having lives of such adventure.
Furthermore, just because they are not supposed to work for money it doesn't mean that the rich and powerful people they occasionally help are not ungrateful. Unlike mercenary contracts, such tokens of gratitude are not negotiated in advance, however. When a merchant lord asks for help in finding his runaway daughter, or the city council requests assistance with thwarting some threat to the city, adventurers are supposed to leap to the task out of the goodness of their heart or sense of patriotism. Outright refusing the task will be seen as the mark of a coward or a cad. What is more acceptable is the adventurer stating that while he would love to help, he is bound by earlier promises that unfortunately make it hard for him to assist at this time. Usually, the other party will then offer to provide all possible assistance to this other task so that the adventurer can focus on this new task with a clear conscience. Smart adventurers will thus prepare to have all sorts of social duties in advance which thus need to be "paid off" by a potential patron.
Once the task is done, it is expected of the patron to present "a token of gratitude". The magnitude of this gift usually corresponds to the magnitude of the completed task - patrons of adventurers who have a reputation for stinginess will eventually find that adventurers usually find a reason to weasel out of their requests. Such gifts are never mere money, but they might be powerful magic items, deeds to buildings, medals and similar honors (in the case of government patrons), and so forth (and again, sometimes these honors are discreetly sold off). They can also be in a less tangible, but no less important form - membership invitations to prestigious clubs or invitations to high society parties, favors of the rich and powerful, access to restricted libraries, and so forth. These are no small things - quite a few adventurers have managed to marry rich heiresses (or rich heirs) this way, and if they should ever land in court because of their crimes, they often have no shortage of powerful people vouching for their good characters.
See Also
Adventure Ideas
Designer's Notes & Resources
Originally I had intended to cast traditional "adventurers" more as outcasts of society - but heck, Urbis is supposed to be a gaming setting, so I figured I should give them a better role to play within society. Hopefully this kind of adventurer is more fun to play than more traditional money-oriented characters - and this way the PCs have more reason to watch their reputation. Plus, having the press follow you around is always useful for some good, clean fun…