We're using SEOmoz and it flags many of our category pages as duplicate content and/or duplicate titles. We use the rel=canonical flag so multiple pages inside the same category refer back to the main page. However, it appears that related categories are getting flagged by SEOmoz and therefore probably by Google.

For example, we have a category for "wooden products" and it has a 10 pages. Each of the pages has the rel=canonical referring back to the main category page. However, at the next lower level, we have a category of "wooden products - under 50 inches." It has maybe 5 pages which all have the canonical reference to the main page.

The problem is that SEOmoz sees the "wooden products - under 50 inches" to be a duplicate of "wooden products" even though they both have different H1, Title, Keywords and Description. A quick check using another tool verifies that these pages appear to be duplicates.

I think the categories help customers zero on on exactly the item they want so I'd like to keep them but I'm afraid we're hurting SEO. If unique H1, Title, Keywords and Description aren't enough, what else can we do to make the pages not appear as duplicates?

Thanks,
Tom