I have had a question from a retailer asking if they can take all our content i.e. blog articles, product pages etc, what is best practice here in getting SEO value out of this?
Well firstly, there is no SEO benefit to either party here unless the retailer provides a link to your site. This can actually cause damage to the retailer's site with regards to duplicate content issues. Forget about canonical tags here, they are not designed to avoid duplicate content issues when copying someone else's content.
My advice would be to advise the retailer to create their own unique content rather than copying your content. They can provide links to product pages on your site but they should try to create unique descriptions for the products rather than copying your content.
With regard to other retailers copying your content, they do so at their own risk as Google could decide to penalise these sites (assuming they haven't already done so). It is best practice to create unique content rather than copying other people's content.
Hope this helps.