I don't *think* the one I want is "prostho Plus" by Piers anthony...

That's Dr. Dillingham if I remember correctly.

I'm trying to find the one about "Gul Dar" - and Miss Schlupe his assistant; They eventually end up on a market planet where Schlupe opens a sub shop

But I can't remember the name of the book! Or the author!

Or maybe I'm not remembering as much on Prostho Plus as I thought.