The Finance Ministry made public a list of 57 Athens doctors who officials believe are guilty of a variety of tax offenses, including failing to give patients receipts for their fees or even recording the visits.
I seem to remember some country instituting a lottery in which they drew from among receipts and gave prizes to consumers who had them; consumers began insisting on receipts and sellers were more reliable about giving them (and reporting associated income). One of the things I've read suggests that in Greece you are frequently offered a "with receipt" price and a "without receipt" price, in which case presumably this wouldn't work as well there.