Google’s John Mueller said that Google may very well treat pages that no longer let you buy a product, i.e. the product is no longer available, as a soft 404. If you try to redirect that page to your home page, category page or an unrelated product, Google may treat that also as a soft 404. And Google treats soft 404s as real 404s and reports them in the Google Search Console.

As an FYI on that, soft 404 redirects are not really counted.

This came up in the Google Hangout on Google+ this morning at the 6:30 mark into the hangout. The question was:

John Mueller responded:

He actually said Google treats these expired pages/products as soft 404s in the past, he said it in April. Of course, I know many SEOs who still use this practice of redirecting these pages to pass the link signals to other pages, but it seems like those link signals won’t pass here?

Here is the video embed, watch it:

Forum discussion at Google+.

Update: Less than an hour after posting this, Glenn Gabe published his case study validating this.