We have a medium traffic site which sells used boats, the site does fairly well for popular search phrases, often ranking on first page.
A common way for people to search is by boat manufacturer, for example "sunseeker for sale" or "sunseeker 33 for sale".
To service those searches, we have search results page with URL's like: "/used-boats-for-sale/sunseeker" and "/used-boats-for-sale/sunseeker/33" (i.e. make and model).
This is fine for common makes but we have a lot of makes where we might have just one which, when sold, then leaves the page with no boats to show. It could then be just weeks till we get another one or sometimes years.
Once a manufacturer has no boats for sale, we automatically remove the link to that page from the site and from the sitemap. These pages are now being flagged as soft 404s in Webmaster tools.
Currently these pages still work and just show a "No results found" message.
I am unsure of how to deal with these pages.
Options as I see them:
Add a "no-index, follow" tag to the pages and continue to remove them from the sitemap. My concern is that when we do get a new boat for sale, the page will not rank again or take a long time to be re-indexed.
Add value to the 'no results found' page - for example, show listings for similar boats. If I do this (which makes sense from a usability perspective), would it be acceptable to leave these pages with an "index" tag?