Just some thoughts (I haven't done much reading or thinking on these issues so possibly this is just to show how little I understand):
One doesn't pay $20,000 for a new car, not get the car because the dealer welched, and simply say: "Boy, his reputation is mud now."
No, one gets a receipt and keys to the car when paying (in whatever way) and drives away in the purchase. The receipt can be one-way anonymous and the car can be paid for in paper cash. (Then there are problems of registration and insurance interfering with anonymity, not relevant to what is discussed here). If necessary I can prove in court that I bought the car, showing the receipt (in theory still anonymously). Now, if I want to pay for the car in on-line cash I guess I could connect to my anonymous bank account with my private key, transfer the money to a bank account of the seller's choice, his bank giving my bank a receipt, and drive away in my new car. So, when buying hardware I only have to trust the digital banking system, not the seller? Well, if the seller is anonymous to his bank also, what can be proved is only that anonX paid anonY the sum Z (or possibly what the purchase was about - a description of the merchandise - if the seller instructed his bank to sign this into the receipt). What if the seller reveales his identity to a court, shows a paper receipt to prove that he has bought the merchandise and claims never to have sold it to me? No one can force him to produce the private key connecting him to the account that received on-line payment. It doesn't help to 'outlaw' paper receipts - still, he can prove that he bought the car by producing the key (password) to an account that paid for it but deny connection to the account that received payment from me. By revealing my connection to my paying bank account I can prove that I 'paid for' the car (possibly time-stamped at a later date) but who is to say that I am not the owner of the receiving account also? Thus, if the seller is identifying himself, an anonymous buyer can use on-line cash to pay for a car and still be 'safe' with a receipt (paper or on-line have similar value in preserving the buyer's pseudonymity). But if both seller and buyer are anonymous, then receipts mean nothing (like in criminal business) but reputations everything. Mats