I was trying to list out all the causes of duplicate content – well accidental duplication.
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 !