Actually these criminals were not really dumb - they just had, errm, bad luck. Both cases happened in North Rhine Westphalia (DE, EU) a few days ago ...
First there was the couple that went to a Bundesbank branch office in Düsseldorf, on April 7, in order to have some Deutsche Mark notes changed into Euro cash. The two handed a total of 16,850 DM over to the cashier ... who then thought the notes were odd.
Turned out that 16,800 DM were counterfeited notes; only 50 DM were authentic. The two were arrested by the police; according to experts, the counterfeits were of "average" quality. Article (in German): http://www.rp-online.de/public/article/regional/duesseldorf/duesseldorf-stadt/blaulicht/553225
And then there was the burglar who, on April 4, broke into a house in Lünen (near Dortmund) and stole precious objects worth more than €50,000. Among the objects that he took with him were about 140 German €10 collector coins, in BU and proof. Now that was a Friday - on Monday (Apr 7) the guy went to a bank in Dortmund and wanted to change the coins into "usable" money. Except that one of the bank employees was the man who he stolen the coins from ...
The "banker" quickly recognized his coins due to the combination of issues and grades. The burglar was arrested; in his apartment the police found even more "looted objects". Here is the police report (note that the "2006" should actually be a "2008") from Dortmund http://www1.polizei-nrw.de/dortmund/Start/article/20080414.html
and here is the same story from a newspaper http://www.fuldainfo.de/cms1/index.php?area=1&p=news&newsid=2542
Ah, sometimes it's not the bad guys who "win".