In Westerns, it's common to see wanted posters with a reward offered in lieu of an organized, coordinated effort by law enforcement to track criminals down; was this an accurate reflection of how the system worked, or a fictional convention? Who would usually be offering these bounties?

by td4999
MimicSquid

While you're waiting for someone to answer your question in particular, you might be interested in perusing the section of the FAQ on the historical accuracy of "Wild West" tropes.