phranque - 1:54 am on Jun 19, 2013 (gmt 0)
"low quality" != "soft 404"
if you are intentionally linking to a url and serving a 200 OK response, it's not a "soft 404".
if your ErrorDocument specifies a fully qualified url and causes a "404 response" to generate a 302/200 status chain, that's a "soft 404".
if a "junk" url request gets a response which very helpfully looks like a 404 page yet provides a 200 response that's a "soft 404".
if a large number of "junk" or legacy url requests get redirected to a single or small number of urls such as the home page or category pages that's a "soft 404".
410 Gone (or 404 Not Found) means the url is gone (or not found), not the product being sold on that url.
going with the bakery analogy, if i show up too late to buy a toasted coconut donut today - sure, it's a low quality experience to be told "come back in the morning when we have some freshly baked" (200 OK).
it would be an even worse experience if the baker told you "we've never sold toasted coconut" (404 Not Found) or "we've stopped selling toasted coconut" (410 Gone).