Some bots checked product page where we had info if product is in stock (although they tried heavenly to bypass any caches by putting garbage in URL). This kind of bots also scaled instantly to thousands checkout requests when product become available with gave no time for auto scaling to react (this was another challenge here)

This was easy to mitigate so it didn't generate almost any load on the system.

I believe we had email notification available, but it could be too high latency way for them.

I'm not sure how much I can share about articles here, but I can say that those were fairly expensive (and limited series) wardrobe products.

Because you presumably want real, returning customers, and that means those customers need to get a chance at buying those products, instead of them being scooped up by a scalper the millisecond they appear on the website.