Canonical on ecommerce pages

[Gordian]

I have seen some competitors using the nofollow tag as well as canonical on all refinements and sorts on their ecommerce pages. Example being if you went to their hard drive category page and refined by 500gb hard drives then that page would have a canonical element to send it back to hard drives page without the refinement. I see how this could be good for control indexation and the amount pages Google crawls, but do you see problems in using the canonical tag this way?

Also I have seen competitors have category page descriptions (describing what that type of product is) on all pagenation and refinements (the exact same block of text on all of the pages). Would this be a duplicate content problem or is it not that big of a deal since the content is only on their site so they are only competiting with themselves.

Thanks for your help

[DanDeceuster]

The canonical tag is precisely to avoid duplicate content issues. If each filter or refinement simply brings up a page of content with a similar block of text and similar display of products as another page, then they don't want them all indexed. Much easier to rel=canonical these pages to the main page so that Google only crawls and indexes one page, not several very, very similar versions of it.

[AlanBleiweiss]

In addition to Daniel's response, I'll offer that having the same description on every pagination version page is not helpful, though if there are enough unique products on each page, and each has a caption and or price, and you optimize each product thumbnail alt attribute, it's not necessarily a duplicate content thing as much an annoyance factor for some users.

Ideally it's best to have a unique description on every page, or only have the full text description on the default category page.  Be sure however to append every page Title, URL and h1 with "Page X" as an additional way to communicate both the uniqueness of each page and for users to know where in the pagination sequence they are.