I've encountered a problem with this NPC. After keyword searching for one item and then typing in a new item to search, the Sales Rep window immediately closes and I can't get the NPC to open again. Various NPCs, Mailboxes and such in the vicinity can be selected but my character is unable to move. Essentially, I'm dead in the water and have to close the game with Task Manager because the other options don't work, either.

For multiple keyword Sales Rep searches, closing the NPC window after each search and reopening seems to be a workaround.