Over the past 35 years or so I've noted that Italians are slow and deliberate when handing back change – but I've never thought that this was a ruse to rip you off.
In the UK, if you purchase an item for say £15 and hand over a £50 bill, you'll typically be given your change of one £5, one £10 and one £20 bill in a single handful. In Italy, for a similar transaction, you'd typically be given a €5 bill, then the assistant would go back to the till and give you a €10 bill, then do the same with a €20 bill.
Just last week in Italy I handed over a €20 bill for a €4.50 purchase. I was handed a €0.50 coin and then a €5 bill. I said thanks you and turned around to leave, before the assistant called me back to hand me the remaining €10 that she'd just taken from the till.
Like Perche I really don't think that Italy is worse than anywhere else when it comes to ripping off tourists. You have to take reasonable care wherever you are – and you'll find 'bad apple' rip-off merchants in most, but not all places.