Ummm... since those are both Profession skills, ANY character class is fine.
If you are wanting them to be really skills heavy (high bluff, diplomacy, sense motive, and intimidate, as well as the profession skill itself) and have a bunch of Skill Focus feats, you could use scholar and take Skill Focus, Negotiator, and so on in lieu of spells.
But, technically, those are both professions and any character class could do them just as well as another.
Many frontiersmen traded with the American Indians, so borderers can be merchants, and so on with all the other classes. Nomads, barbarians, all of them might have a need to trade. African tribes traded slaves and goods - and they might be classed as barbarians. Commoners, of course, can take professions.
Ultimately, any class is fine. Just take the Profession (merchant) or Profession (slaver) skill, and back it up with some other skills and feats as appropriate.