[blhack]

Hmm, I think it's smarter than that.

Every year around burning man time it "notices" that I'm buying supplies for burning man, and starts recommending me things like baby wipes, which are completely unrelated (naively) to things like lag screws, rebar pullers, etc.

[ergothus]

I suspect that's the impact of other burners also shopping, generating a good list of "people who bought A and B also bought C, D, E...". As soon as you hit A & B, you trigger the rest, while the average person doesn't.

[freyr]

It could just be recommending things you buy seasonally, without recognizing the relationship between the items.

Try buying lag screws, rebar pullers, etc. in 6 months and see if it recommends your baby wipes.