I've seen QR codes (as well as URLs and input codes) on supermarket receipts in the UK. They're for reviewing the service, checkout staff, etc more than any product.

Google Surveys do a "scan in your receipt" thing to solicit place reviews.

Verifying customers only verifies that one thing. It doesn't stop fake reviews of "real" customers (happens a ton on Amazon), or influenced reviews "Leave us 5 stars and we'll give you a gift voucher", or all the other crap that spoils real reviews.

I occasionally wonder if state-funded reviewing might be a useful additional data point. "This does what it claims, appears well built". Obviously applying that to every product sold might be a stretch, but expensive essentials (eg white goods) would be a good opening target.