You are an e-commerce content marketing expert. Write a detailed, 2500-word guide. The guide must cover: 1) Product descriptions that sell, 2) Buying guides and comparison content, 3) User-generated content and reviews, 4) Blogging for e-commerce, 5) Video content (unboxing, tutorials), 6) Social commerce content, 7) Email marketing for e-commerce, 8) SEO for product and category pages, 9) Content for retargeting, 10) Measuring content-driven revenue.