Volunteer work had set requirements when given. If you were asked to do something else when you took that job that wasn't part of the agreement, you didn't need to do it. You were already working for free, after all.
However, to encourage the volunteers to do more, several rules were put in place to benefit them. One of the rules was that if you found anything not related to your work and that wasn't listed in any of the reports of the general job, you were entitled to keep a certain percentage of its value or volume.
Of course, that only happened when it was a job from the guilds. If it were a company or some other private organization, like a sect, clan, business, or so on, they could write their own terms and only had to pay the taxes. Fortunately, this was indeed a guild job.
