Sometimes you might want to have Google and other (are there any other?) search engines not show certain products in your site. This is where noindex is worth some value. Have a read of this Google Support page.
With that in mind, we know that any page with noindex will eventually be removed from the Google results pages. It might take some time, but it will happen when the Googlebot hits your page and reads the noindex tag.
Took me all of 10 minutes to code up a quick and easy mod to enable shop owner to set each product to index or noindex. Default is, of course, index!
An extra red/green selector;
red = noindex
green = index
No outward change, but looking at the underlying code of the page, this is added if a product has that red selector;
This is done using a Header Tag Module
The benefit to this is that these modules are drop in, so there is not any need to amend the code of the product_info.php page.
Be aware that some people giving advice at the osCommerce sell SEO services and therefore are going to try to confuse the hell out of you by spouting shite.