Here is the list to date
- Inconsistent URLs and links, especially search results or inventory via different attribute routes
- Similar products or bundles of products with similar description, this can be on your sites of resellers
- Print friendly pages inc. white papers, pdf downloads.
- DNS errors ie. no http:// to http://www etc or https !
- Content management systems who use session cookies in urls
These all produce Errors – and effectively your are ‘pissing in your own pool’. And risk getting duplicate content penalties – even though – you probably don’t realise you have done it. The good news is that all of these can be fixed fairly easily.
As I resolve more here – I will add to this list – send me more if you have them !