This General Supplies guy is in a level 18+ area, and only sells level one stuff.
Hopefully this will be changed (unless you have to finish the end quest to get this, which I haven't, similar to the Restless Isles)

Also, he has two dialog options, both of which seem to indicate you will bring up the store option, but only the first option does
  • I would like to trade
  • Yes, show me your supplies