Originally Posted by
Gamecock
Back to your origninal question, most airlines frown on purchasing miles from companies that sell miles. Don't make the mistake of getting involved in any of these companies. Points.com however, is an accepted source of bartering miles among several programs.
Though you're right (don't buy tickets from third parties), I think the OP's question was just inartfully phrased because of his lack of familiarity -- you don't need to buy miles "from companies" because you can get them from airlines directly. I think he just didn't know that.