> Here in Italy the big issue is that many business will just not declare cash transactions. It's pretty common not to be given a receipt when buying a coffee and often when you visit a doctor they'll say: do you want the invoice or a discount?

1) Require receipts for all transactions.

2) Offer 10% of recovered cash for anyone you report who doesn't follow #1. Add the penalty on top of any recovery [e.g. Current Fines + 10%]

3) https://www.irs.gov/pub/irs-utl/cashchapter4_210632.pdf

4) Taiwan-style receipt lottery [ http://www.tealit.com/article_categories.php?section=living&... ]