I think the comment was that if they buy a vacuum and don’t like it, they return it and buy a different one. So if that happens 20% of the time, that next month has a much higher chance of buying “another vacuum” than the average month.

Also, I bought my parents a Roomba because I liked mine, so that can happen too.

Several years back a bunch of us pet-owning friends wound up round-robin gifting the same model SpotBot carpet cleaner to each other, because it was something we all agreed made our lives better. Nothing weird about it at all.

The fact that you had to preface this with you and your friends being pet owners kind of does make it a special case. You being suggested this vacuum cleaner by Amazon after buying it also doesn't do anything for you in this scenario because you bought the same one for your friends, so the recommendation wasn't needed. I think people are losing sight of the original argument which is that Amazon's recommendations can sometimes overemphasize recent purchases with very little context around what the items are.

Yeah, but everyone is "special case" in retail.

A vacuum cleaner would be a great housewarming gift, for example.

I did, not a month ago. Nothing strange about the process whatsoever.

It truly is a gift that sucks

I've done it before: shortly after I bought a robot vacuum; I gave the exact same model as a birthday gift