MisterT - 7:22 am on May 16, 2010 (gmt 0)

So people do this deliberately? As a shopper, it's one of the most annoying, off-putting things to click on a SERP for a specific product and then not be able to find it. Believe it's against Google's Webmaster guidelines as well - what do you do with that inbound non-robot traffic that clicks on that SERP? Redirect it somewhere else?

Yes. Lots of stores, including big sites like Amazon. Just because the product is not for sale does not mean the page has no value. There is info about the product, reviews, and links to similar related products.