Automated Price Error Detection

I need a lightweight bot that continuously scans the sites I specify—general-purpose e-commerce marketplaces, individual retailer stores, and major price-comparison portals—and flags three very specific anomalies:

• out-of-stock items that still display a price
• discount calculations that don’t add up (e.g., “50 % off” shown but only 10 % applied)
• obvious mis-priced listings (extra zeros missing or added)

The moment any of those conditions appears, the bot must fire off an instant alert. E-mail is fine, but having the option to plug in Telegram, Slack, or a simple webhook would be even better.

Core expectations
– Code in Python or another language you’re comfortable maintaining on a small VPS.
– Clean, well-commented logic so I can tweak thresholds or add new URLs without digging through spaghetti.
– Reasonable cadence (near real-time is ideal, but let’s balance that against rate-limit rules).
– A short README with setup instructions and the single command that starts the monitor.

I’ll test by feeding the script a sandbox list that contains known bad prices; if every case triggers an alert—and only those cases—you’re done and paid.