I use Expert for people that are highly skilled at several things, or have a job that has several parts. No real need to use Expert for things like carters, bakers, fullers, latrine diggers, pigboys, and the like; that takes care of hundreds on midieval jobs like charcoalers and stuff like that. Just Google for 'midieval jobs' and you'll get several long lists.
Generally, the top line of the various Craft X professions will be Experts: leatherworkers, smiths, glaziers (glass makers), jewelers, tailors, woodworkers, etc.
The reeve or forester will also need to be an Expert if he's not a Ranger.