Here's another point worth considering, if you happen to be among the "generous souls who offer their services for free" crowd. There are several professional artists within the guild who derive their livelihood from their art. In addition, there are likely others here who would like to learn how to derive some residual income from the hobby they love, and perhaps even become professional artists themselves. Map commissions present an opportunity for such guild members. Yet if other members of the guild are willing to take on unpaid map commissions-particularly if those members happen to be amongst the more talented of the guild-this would seem to serve as a disincentive for those requesting maps to offer financial compensation for the work that they are requesting. Why would someone pay a journeyman cartographer, a guild artisan, or even a professional artist to create a map that they could just as easily have had a guild community leader create for them for free? So by offering to take on unpaid commissions, these guild members may be inadvertently stifling important financial prospects for other guild members. I'm sure that this is not what is intended, but it might nevertheless be an unanticipated consequence of offering one's services for free.

Cheers,
-Arsheesh