I experienced a rather annoying DCC scam at my wife's doctor's office in Shanghai. It was a $9k bill (neo-natal care and prepayment for hospital), and the invoice came in USD. We had previously paid in CNY at this office, but we tried every POS machine and could only get USD. I ended up using my AMEX and paying the int'l transaction fees, but I unwilling to eat the ludicrous FOREX rates offered by Bank of China and China merchant's bank. In this case, at least, the whole finance staff of the hospital claimed to be uninformed.
If it was simply a scam by the teller, it would be easy to overcome. The fact that the banks set the machines in such a way to prevent local currency transactions makes it so much worse to do business. I just stopped using merchants with DCC issues, though the staff was often unable to understand exactly why...