If you follow a link from a search engine like Google, for a listing that is no longer available, in some cases it will produce a page which shows the address, but no photo or listing details.

The address is produced from the URL, but the fact that the listing no longer exists means that no details can be pulled from the listings API.

Some clients have expressed it being preferable/less confusing for that to go to a "listing not found" message instead of reporting the address of the listing.