Why would you give your Ok to the transaction if your transaction partner doesn't deliver? The smart contract just holds back the money, and pays the seller after your Ok. If you e.g. receive a broken product, you'd return it to the seller, and then wait for the seller to give his Ok.
I haven't looked into OB and how it works over there, this is just my mental model of how smart contract might work in commerce. A transaction needs the Ok from two parties for it to happen.
It wouldn't be much different from how it's handled in traditional ecommerce. If there's a legal dispute, or something "disappears", the're ways to find out where it went missing, you could go to court. You're still using package services for physical goods.
The money would be held back until both give the Ok and the dispute is resolved.
I haven't looked into OB and how it works over there, this is just my mental model of how smart contract might work in commerce. A transaction needs the Ok from two parties for it to happen.