Write a Python Script That Checks Your Product Feed for Price and Stock Errors Before Black Friday

You are a senior Python developer who builds small, reliable data checks for online stores. Before Black Friday, I want a script that reads my product feed export and catches the errors that cost sales or get products disapproved: wrong prices, sale prices higher than regular prices, items marked in stock with zero inventory, missing images, and broken product links. Write code that runs on a normal laptop with Python 3.10 or newer. Do not assume field names, file formats, or platform APIs I have not described. If something is unclear, list it under [QUESTIONS] before the code.

My feed format (CSV, TSV, XML, or JSON) and how I export it: [FORMAT]
The exact column or field names for id, title, price, sale price, currency, availability, quantity, image link, and product link: [FIELDS]
My store platform (Shopify, WooCommerce, BigCommerce, custom): [PLATFORM]
Rough number of products: [SIZE]
Sale rules I actually plan to run (for example 20 to 30 percent off selected collections): [SALE RULES]

Requirements:
1. Use only the standard library plus requests, unless I say otherwise. Explain how to install requests.
2. Parse the feed and normalize prices (strip currency symbols, handle comma and dot decimals) without guessing the currency.
3. Flag rows where: price is missing, zero, or negative; sale price is higher than or equal to price; the discount is outside [SALE RULES]; availability says in stock but quantity is zero; quantity is positive but availability says out of stock; title or image link is empty; the same id appears twice.
4. Optionally check that product and image links return HTTP 200, with a flag to turn this off, a polite delay between requests, a timeout, and a limit on concurrent requests so I do not overload my own store.
5. Write results to a CSV report with id, title, problem type, and the raw values, sorted by severity, and print a short summary count per problem type.
6. Exit with a non-zero code when critical problems are found, so I can run it on a schedule.
7. Add clear comments and a short usage example from the command line.
8. Do not change or upload anything. The script only reads the feed and writes a report.

Deliverables:
1. Questions about my setup, if any
2. The complete script
3. How to run it and read the report
4. A short checklist of what to fix first before the sale starts