Quote from: Monster Tent on September 11, 2012, 02:36:07 AM

I cant believe people send anonymous individuals thousands of bitcoins without even requiring a simple acknowledgement that they received a good or service.

A pseudonymous digital currency certainly changes things doesn't it? This is also being discussed in another thread. Here's a excerpt:

Quote from: Stephen Gornick on September 11, 2012, 07:27:45 AM

It definitely isn't needed for buying a donut:
- http://www.youtube.com/watch?v=X53ksjejmns

I probably don't need a digitally signed payment request from Amazon because if their payment page didn't acknowledged my payment my next action is to contact their support. If their system is compromised where I get a fake payment acknowledgement they'll know about the problem long before I notice that nothing showed at my door.

But for transactions where where there is a time component, such as where the payment creates or extinguishes a debt, that's where in practice this protocol becomes more needed.

With most traditional non-cash payment systems, we don't need a receipt in many instances because the payment system holds identity. When I send a check for a car payment to the bank, I don't need a receipt, If there is a dispute then if that check was cashed that's my proof of payment.

For relatively insignificant amounts of money for transactions both cash and pseudonymous digital currency seem to work just fine the way they are currently used. If I give you cash and you don't give me my donut, chances are right there and then I'll be getting my cash back -- though it may involve me making a stink in public about it.

Quote from: Monster Tent on September 11, 2012, 02:36:07 AM

A receipt should be signed and dated and have the person/business details you got the service or good from. In the event of a fraud you will then have something to show the relevent authorities. Dont go and report a bitcoin theft without this proof because the police will simply fob you off.

With Bitcoin, there doesn't even need to be an action post-payment. Here's why:

Quote from: Stephen Gornick on September 11, 2012, 07:27:45 AM

That's when I'm going to want them to give me a signed message that not only says what Bitcoin address to send my payment to but the account number that the payment will be applied to as well.

With the blockchain providing the proof that payment was made, this signed payment request from before I pay is all I need then to later prove that I made the payment.

Gavin's addresses how in the future Bitcoin might address this:

Quote from: Gavin Andresen on September 10, 2012, 12:22:11 AM

We need a payment protocol with non-repudiation built in.

See https://gist.github.com/2217885 for a multisig version (the singlesig version is simpler, but the merchant <-> customer communication will be the same).