When manufactures started making black Friday specific items. They are cheaper and worse quality than average, designed to look like but offer lower tiers of high demand products. TVs are a great example, they make versions of regular TVs that are worse quality but look like the year round product. Made to be sold during sales. But of course that creates a floating stock of stuff that will never sell for the price of the regular product, and also have to be made and ship a bit before the actual sale dates, extending the sale over time.

For sales on Amazon you can check the price history on Keepa. They have a browser extension but avoid it, it’s problematic privacy wise.