Well... what an adventurer does to keep himself alive? Anything? That might be correct, but surely they must specialize in something, otherwise they would be simply be called wanderers.
If we go with the trope, adventurers explore, that's the whole point of their existence. They are glorified archeologists and travellers, by definition they go to the fringes of society and look for things of value, and whats of value there?
Artifacts and information. The same as it is in our world.
There is no intrinsic problem with a guild of adventurers, specially in fantasy where there are always old things lying around with so much power that can turn the tides of entire wars or cause an apocalypsis, having an organization managing those items is actually a necesity for both increasing the chances of sucessfull parties to protecting those artifacts, profit is not a problem since these guilds can turn into a mafia quite easily(pay or we release this old artifact that holds an entire army of the undead in your lands) or an actual service(provider of powerfull tools) or public utility(museum), and with money there is organization.
The problem is in naming. Adventurer is too broad, for it only means "those who do adventures" and adventure is not a well defined concept.
Except if you go the other way around, and make sure that culturally it makes sense that an adventurer stops meaning that, and instead means wathever you want your adventurer guild wants, I mean, just see how feminists throw a hissy fit when you suggest that "egalitarian" describes their movement better.