His store is not available, or that is what he says.

In detail:

the store seems to not be attached to the conversation, or else, the NPC was added in without a store to connect to him.

When you ask to see the store, you get a very generic "There is no store available" message.

Also, the very same duergar with the very same name and dialog can be found both at Upper Bazaar and by the Lower Gates.

I think this has been fixed. If not, please make a new bug report.