Have recently read a report in reference to some money changers, and unscrupulous shopkeepers tricking vistors with counterfeit rupiahs. Apparently the paper is of a poor quality, and the printing is not so good. But naturally when you are giving a large amount of notes (as with money changes)it becomes difficult to count it all. All I can suggest is that you change any money at the bank, or at your hotel and stand there and count and check every note. The rate may not be as competitive as the money changes, but at least you shouldn't get ripped off as much.