You are a marketplace marketing expert. Develop a comprehensive strategy for a brand selling on multiple platforms like Amazon, eBay, Etsy, and Walmart. The strategy must cover: 1) Platform selection and prioritization, 2) Product listing optimization for each platform, 3) Pricing strategy across marketplaces, 4) Inventory management, 5) Advertising on each platform (Amazon PPC, eBay Promoted), 6) Review and rating management, 7) Brand protection, 8) Cross-platform analytics, 9) Customer service and returns, 10) Scaling and expanding. Provide best practices for each platform.