What should I do if someone offers me a clearly ink-stained or a bleached/discoloured euro banknote?

An ink stained banknote is most likely a stolen one. Refuse to accept the banknote and simply ask for another banknote. The ink-staining on the banknote may originate from an anti-theft device – also called intelligent banknote neutralisation system (IBNS). This cash protection system has marked the banknote during a robbery when criminals took the banknotes out of an ATM or another container which was protected by an IBNS. As the criminals will try to remove the IBNS ink-stains by washing or bleaching, please refuse also such bleached or discoloured banknotes.