>What's a consumer's interest in asking for a receipt? Especially when you can get a discount instead?

Because some people need an alibi. Patrice Oneal put it best: https://youtu.be/RrBPmoIAyts?t=100

> require receipts for all transactions, allow consumers to report business who do not give receipts

You incentivize compliance through monetary awards for reporting offenders.

So I guess I'm curious about how Italy's system works then? It's an empirical question, how much money would I have to be offered to turn on a system of convenience and perhaps monetary discounts? (I'm not considering the downside of off the book transactions as a consumer, I realize).

I'm assuming for it to work in Italy, you would have to make the reward for reporting non-compliance higher than any discount a business owner could offer.

It would presumably need to be several orders of magnitude higher as I would probably buy more donuts than I would submit non-compliance reports. And let's not forget it's the government that's running this - they don't necessarily need to turn a huge (or any) profit to make this work in the long term.

  Donut with receipt:    $  1.49
  Donut without receipt: $  1.00

  Taxable reward from
  gov't for reporting
  non-compliance:        $500.00

The government would also have to worry very little about profit because the fine for not giving customers receipts could be higher than the reward for reporting non-compliance, which makes the system self-funding.

If I find dead insects in my donut, I'd like to have evidence that I actually bought a donut from them.

What are you going to do with that evidence that walking back to the shop won't accomplish? If I'm too far away, I'll throw the donut in the trash. If I'm nearby with nothing better to do, I'll stop back and ask for a refund.

Nothing about that practically requires a receipt. If I'm denied a refund when I go back with an insect-laden donut, I can make enough ruckus in the shop to get my entertainment value's worth. I don't really need the $0.75 anymore than I need the donut...

Actually I would send it and a photo of the donut to the local health and safety regulators. I don't care about how much I spent; I care about not having it happen again.