As I posted in another thread (that I do not want to derail further), I think that many of the later Ars Magica supplements have seen a proliferation of Craft and Profession abilities, against the letter and spirit of the Corebook: namely, that Craft should deal with "handiwork" (so no Craft:Poetry), and that Profession should cover other jobs not covered by existing abilities (so a fighting grog should not have Profession:Soldier or whatever).
To be fair, the stipulation that Profession should not overlap with existing abilities is never made explicit even in the Corebook, and in fact of the handful of Profession examples a few might indeed violate it. But I think it's a fine stipulation: the portion of being a Factor that is about haggling should be covered by Bargaining, so a character can teach it to someone in another trade, and use it himself if switching to another trade. Only that which is fundamentally "unportable" should have its own Profession. This also means that to be an effective merchant someone should have several abilities rather than relying just on Profession:Merchant, just like to be a well-rounded craftsman you need many more abilities than actual craftsmanship.
And I realized that in this sense there seem to be really few Profession:X abilities, so few that each might deserve its own entry and name. A grand total of three, in fact (perhaps with names different from the ones below), each about as broad as Music.
Farming: you know how to manage land, so as to preserve it and harvest its vegetable resources. You know how to assess and improve the quality of soil, how to till, grow crops, harvest and store them. You also know how to assart. Example pecialties: lumberjack, any one area or crop.
Seamanship: you know how to handle any boat, raft or ship and how to handle yourself on one. You know how to fish using nets and lines. You can perform emergency repairs and navigate using the sun and stars. To use or draw maps or a sextant, and to compute complex routes you also need a score in Artes Liberales, however. Example specialties: fishing, sailing, any one area.
Housekeeping: you know how to manage a household. You can wash, clean, sew, make beds. You know how to store food and serve at a table. You can also keep a simple budget of income and expenses, even though for any complex mathematics (or even simple reading and writing) you need Artes Liberales. Example specialties: washerwoman, thrift.
I've tried to think of as many "jobs" as I could, and the associated primary ability (that used in the formula for Labor Points), and they are all covered. Management roles, whether managing a ship, a company, an army or a really large household also require Leadership, as per C&G rules. A modicum of Bargain is required to monetize your skills (again as per C&G rules), Intrigue covers politics as well as "shady" aspects of a job such as smuggling, Artes Liberales covers reading, writing and math etc.
Soldier, Archer, Tourney knight, Warlord: Weapon ability (see Lords of Men)
Merchant, Factor: Bargain
Poet, Storyteller: Language (as per Corebook)
Fisherman, Sailor, Ship Captain: Seamanship
Sheperd, Falconer, Marshal, Stable boy, Teamster: Animal handling
Prostitute, Gambler: Carouse
Innkeeper: either Carouse or Housekeeping, depending on the establishment
Courtesan, Bureacrat: Etiquette
Washerwoman, Housewife, Steward, Servant: Housekeeping
Bailiff, Farmer, Lumberjack, Reeve: Farming
Apothecary Physician: Medicine (see A&A)
Barber, Surgeon: Chirurgy
Jongleur, Cutpurse: Legerdemain
Lawyer: Civil or Canon Law
Hunter, Trapper: Hunt
Laborer, Porter, Longshoreman: Athletics
Miner, Charcoaler, Baker, Miller, Smith, Craftsman (including artistic ones such as painters): Craft
Scribe: Artes Liberales; alternatively, you can take Craft: Painting (which covers Illumination too) in which case you can copy texts but you cannot read them. Many texts in the middle ages were copied by monks who could not read them, and replicated letters as one copies a drawing.