That creates a bit of a catch-22 for the company. If they show people the code, it's hard to keep people from using it, but buying something sight unseen makes some people (like me) a little nervous. It's like buying a mystery bag, or playing the lottery, neither of which I would ever do.
If I were them, I'd probably try and get some testimonials from some respected developers - get a few people with some know-how to say "yeah, their code is good". I think it would make people more comfortable about shelling out cash to buy source code they can't look at first.
Note: I've heard from someone who has bought one of the source code projects, and the feedback was positive. This person said the code was "well organized" and "clean", though he hadn't had a chance to look at it in detail yet. That's definitely good news for the Tausendstern folks, and for their potential customers. I've decided to purchase the package and take a look for myself - I'll give a report here when I do.