On the train nearing Konstanz station an older, well-dressed gentleman overheard our conversation that we did not have accomodation for the night. He offered to help us to take us to a small and inexspensive family-run hotel in Konstanz. After a short bus ride he took us to the hotel and we were given a small and clean room. We found a chart in the room and to our horror we saw that the room rate was twice what we could afford. We walked down the corridor and spotted the gentleman knocking back drinks at the bar and chatting with the owner (probably laughing about the 'suckers'). We grabbed our bags and left undetected via the back door a little wiser.
You surely didn't register and then run away did you? The chart on the back of the door is the maximum they can charge but usually bears little or no relation to the price you actually do pay.
You wouldn't have let them register you for a room without inquiring to the price? I don't think that you were scammed. The only scam I see is a registered hotel guest doing a runner.
Is there a reason that you didn't bother to ask the owner what the price was? Odds are that the rate was significantly less than what was posted. It is unlikely that anyone was trying to scam you.
The first time I saw the rate card in a hotel room I nearly fainted. But I asked the receptionist what the rate was and he confirmed that it was the rate he quoted me.
Somewhere in hotel-world there's a forum with posts about guests who run out on their bill.