<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">
<div>A merchant can always refuse the payment and refund it if that's a practical problem.</div></div></div></div></blockquote><div><br></div><div>No, they can't, at least not in bitcoin-qt: when the user pokes the SEND button, the transaction is broadcast on the network, and then the merchant is also told with the Payment/PaymentACK round-trip.</div>
<div><br></div><div>Allowing merchants to cancel (e.g. having a PaymentNACK) makes implementation harder, and brings up nasty issues if we want to allow CoinJoin or CoinJoin-like transactions as payments to merchants. Bitcoin-Qt ALREADY allows you to pay several PaymentRequests with one transaction; handling the case where one merchant gives you a PaymentACK and another gives you (or wants to give you) a PaymentNACK is a nightmare.</div>
<div><br></div><div>--<br></div></div>Gavin Andresen<br>
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