I read the last line of your post Pfeiffer... and like I mentioned earlier (if you saw it), sometimes people cannot see what is in front of them... the more astute will search for answers the point and click generation need it obvious and the more obvious options there are, the more chances they will use those options.
Now, obviously, earlier when I said about me being able to contact customers for whatever reason, the smart seller would not spam people (personally I abhore spam), however a one off email or within-Shapeways-messaging-system thanking a customer for their purchase and asking for feedback is not spammy and depending upon the answer could lead to bigger things.
Currently the only method for customer and designer interaction is via Shapeways messaging system, as you rightly say, if the customer chooses... I would also add 'if the customer sees'... the link for contact.
So going back to my issue with customers not realising what my model incorporates... they did not see the title and they did not understand the terminology in my description. Me being able to communicate directly with those customers gives me the opportunty to appease without my model potentially causing Shapeways some bad rep.
As a designer, I'm looking out for myself, as a customer of Shapeways, I'm trying to look out for them... I don't mind taking flak, but I certainly feel uncomfortable knowing that something I could have avoided maybe causing someone else flak.
Don't want to argue with you, that's just the way I am