No, that's correct. It would have to be the case that anyone could discover all the listings, if any random buyer is expected to be able to find any particular listing. The key is a third party wouldn't know which products the transactions are involving, nor who the buyers or sellers are. Without the long term identity key, someone analyzing the block chain wouldn't know that Buyer X was involved in transactions 11386, 16882, and 23319. Not even the escrow agent would know that.