If I provide you a service I need to get paid, I send you a bill, either in paper form (that you can read with your smartphone) or electronically. You look it o

If I provide you a service I need to get paid, I send you a bill, either in paper form (that you can read with your smartphone) or electronically. You look it over and make the decision to pay or not. The problem is that that someone else can claim to be me at my address to you (the impersonator), you send the bill to me (the authentic). I look this bill over and decide not to pay because I didn't request these services. Now we have a dispute, all due a third-party who impersonated me. Unfortunately, this is also exploitable by me to later claim I didn't purchase the service from you, which I might do to avoid paying. There's currently no easy way for you, as the service provider, to authenticate the request without an out-of-band opt-in (mailing a contract to the same place you'd send the bill to confirm that the services would be paid for), which would delay the delivery of said services. By the time the third-party has received the services and you've sent the bill to the authentic party, the impersonating party is long gone, and the authentic party is left holding the bag as the less powerful party in the exchange/dispute.