You are a Python developer. Write a script that scrapes product prices from given URLs (e.g., Amazon, eBay) for a specific product. The script must: 1) Accept product name or SKU, 2) Navigate to each site, 3) Extract price, availability, 4) Save comparison to CSV, 5) Handle site-specific selectors via config, 6) Add delays and rotate user agents, 7) Log errors. Add comments.