Yes, duplicate content (product descriptions) and thin content (hardly unique content).
And also because imo it does not make sense to let visitors make an extra click by letting them click through to a details page on your site and then let them click through to a page with the same info on the merchant's site.
On my personal websites I never display product detail pages, product descriptions and price. I only display category pages with products immediately linking back to the merchant's site.
By providing "incomplete" information the visitor must click through (= click your affiliate link) to the merchant's site to find out more about the product. After all that is your goal as an affiliate (getting that visitor click through to the merchant's site).