I also came up with an equivalent to vendor reviews. Since most vendor reviews are 5 or 1 in practice, we can reduce that to 1 or 0, or signed (endorsed) or not. Vendor reviews can be based on a web of trust of anonymous transaction signing. When transactions are successful, buyers can sign them, even though others don't have their keys. They can still see that many seller transactions were signed by many anonymous buyers. So, when the seller provides his identity key, you are exposed to the number of transactions, the prices involved (to protect against sellers making 100 purchases of $1), the number of resolution disputes (through a special mark on the transaction), and the number of endorsements (or anonymous key signings). The key difference is that you can't prove what the products in any of the transactions were.