What is meant by pursuing gain with gain? Leading on from this answer - in the Maha-cattarisaka Sutta  it identifies wrong action in one's livelihood as 


Scheming
Persuading
Hinting 
Belittling 
Pursuing gain with gain


What is meant by pursuing gain with gain? It is a problem with the translation that makes it unclear or have I just missed an obvious interpretation?
My first thought was that it meant usury, but apparently Buddhagosa defines it as, 


  'Herein, what is pursuing gain with gain? Seeking, seeking for,
  seeking out, going in search of, searching for, searching out material
  goods by means of material goods, such as carrying there goods that
  have been got from here, or carrying here goods that have been got from
  there, by one bent on gain, honour and renown, by one of evil wishes,
  a prey to wishes—this is called pursuing gain with gain' (Vbh. 352-
  53).


... which I think implies being a merchant (buying here and selling there), or more generally capitalism.

Note that that sutta is addressed to monks.