I don't buy stuff on Amazon just because it's on sale, but I do have a few things in my Wish List that I want to buy but only when they're at a price I'm happy with; many of them have been there for years.

Whenever I see a price change, and I'm not ready to buy, I add a note in the wish list notes with the current price, essentially tracking every price I see it at "by hand".

During sales I check back, and for ~90% of items in my list, they're higher not just than the lowest price I've recorded, but also many of the previously higher prices.

At this point I'm not even bothered about really ever buying much of this stuff on there, but it's fun to track the data even at a small scale like this.