The Collaborative International Dictionary of English v.0.48:

Jobbing \Job"bing\, a.
   1. Doing chance work or odd jobs; as, a jobbing carpenter.
      [1913 Webster]

   2. Using opportunities of public service for private gain;
      as, a jobbing politician. --London Sat. Rev.
      [1913 Webster]

   Jobbing house, a mercantile establishment which buys from
      importers, wholesalers or manufacturers, and sells to
      retailers. [U.S.]
      [1913 Webster]