Targeted Ads -- How Do They Know?

[hollohas]

Half the targeted ads I see are for stuff I already purchased. That's a HUGE waste of advertising money to target people who already have the product IMO.

[izzy]

Half the targeted ads I see are for stuff I already purchased. That's a HUGE waste of advertising money to target people who already have the product IMO.

That always cracks me up. Especially when it's something you won't usually buy twice like a water heater.