Mistake 1: Pointing multiple pages at one canonical
If every product variant canonicalizes to the parent, you're telling Google none of the variants should exist. You lose the long-tail rankings entirely.
Mistake 2: Canonical chains
A→B→C canonicals confuse crawlers. Always point directly to the final destination.
Mistake 3: Cross-domain canonicals gone wrong
Canonicalizing to a domain you don't own — accidentally — happens constantly during migrations. Audit every release.