Well, if you buy an uncut sheet, then cut that yourself and sell the single pieces as supposedly valuable errors ... There have been many auctions and sales of such pieces; here is another one that ended at €36.50 earlier this year:
http://cgi.ebay.com/ws/eBayISAPI.dl...350302383200You can buy such a sheet here for example (in German; images had to be modified at the request of the Bundesbank):
http://www.geldmuseum-shop.de/websh...eldbogen.htmAnd this page (in German) explicitly states that such "errors" are self-made:
http://sammler.com/mz/gs_news.htm#InfosWhether the info that only €5 and €10 notes are available as sheets is correct or not I don't know. But I would not buy them ...
Christian