The best time to show you vacuum ads is right after you buy a vacuum because:

* You have concrete intent

* At a 5% return rate (pretty low), that's 5% you're going to buy the alternative

I hear that that explanation a lot.

I'm not sure I buy it.

As for why:

1. I don't have much data except myself but I can't remember buying from those ads.

I can remember smiling at them a lot though.

2. That wouldn't explain why I get ads for the exact same product I bought.

Here's another argument I remember from marketing at engineering school:

Some marketing is justified even after the customer has bought -especially with expensive items - to make them feel like they did the right thing (which in turn should make them less likely to return it.)

That's the problem with advertisement. It's ok to annoy 95% to sell to 5%.