If you need a bike worked on, you do not have a lot of choices in the Joplin area. Probably the best around it X-treme Mechanix on 7th street. They have a few used dirt bikes as well if you are looking for one. They service dirt bikes, four wheelers, and I think even jet skis. They do pretty good work with a decent turn around time. They also have a few parts in stock as well some accessories if you need them.
Check them out if you like dirt bikes.