It's the merchant's signature. The buyer's info isn't part of the receipt as I envision it. It's necessary for some of the functionality I mentioned but not all.

Also you're assuming the receipt from one transaction follows the item. That's not necessary. Every transaction gets a new receipt. But you would want a history of receipts for a Rolex or car.

Picture this, I submit the item to Craigslist with my receipt. It's not posted, but Craigslist verifies it and puts a check mark on the post.