Short version: ShopCheck collects nothing, sends nothing, and has no server to send it to.
On Amazon search pages, Instagram, and pages that look like online stores, ShopCheck reads the text of the page you're already viewing in order to find brand names, Sponsored labels, link destinations, and the signals listed on the home page. That reading happens inside your browser and the results are drawn onto the same page. Nothing is transmitted.
Your settings (strictness, dim/hide/label, toggles) and your Trusted and Blocked lists are saved with Chrome's extension storage (chrome.storage.sync). If you're signed into Chrome, Google syncs that storage between your own devices, the same way it syncs bookmarks. ShopCheck itself has no access to that sync and no copy of it.
None. The extension makes no HTTP requests, loads no remote scripts, and fetches no remote lists. The brand list ships inside the download and only changes when you install a new version.
The store check has to run on whatever store an ad sends you to, which could be any domain. Chrome has no permission narrower than "all sites" for that. The script exits immediately on pages that don't look like a store.
This site is static files hosted on Netlify. It sets no cookies and runs no analytics scripts. Netlify keeps standard server logs.
The extension is twelve plain-text files. Open any of them in Notepad, or search the folder for fetch, XMLHttpRequest, or http.