I have noticed that some QR codes presented by merchants for payment encode not only the destination address, but the amount of the transaction. This is, I am sure, meant to be a convenience for the buyer. However, it would be quite easy for an unscrupulous operator to encode some much higher amount than the legitimate price into the QR code, thus scamming an unwary customer. In a system wherein charges are difficult to reverse, and wherein many wallet programs lack a confirmation dialogue box, it would behoove all to be wary..