Another alternative is that perhaps people are clicking on ads for things they already own. I mean, let's say there's a 1/5000 chance that a random person is going to buy a SDXC card. You go ahead and buy one. After the purchase, statistically does your likelihood of buying another SDXC go up or down? For some people, they've fulfilled their SDXC quota, so now their likelihood is zero. For other people, they may be in the market for SD cards generally, so they will be more likely to make a second purchase than a random person. Or, after having bought one, they'll want to buy another one as a gift. Or they're looking to return the original and buy a cheaper one at a sale price. Just the fact that they have equipment that takes SDXC cards means they're more likely to buy another one than a random person.
Same thing with a pool filter even. If you live in an apartment, or if you're a minor, or you don't own a pool, your chances of buying a pool filter are extremely low. So the fact that you just bought a pool filter puts you in the narrow group of people who would potentially have need for another pool filter. Even though you just bought one, you're still more likely to be a customer than a random person. Hence, generally speaking, sending you ads for the same thing you just bought may be a rational choice for the advertiser.
Same thing with a pool filter even. If you live in an apartment, or if you're a minor, or you don't own a pool, your chances of buying a pool filter are extremely low. So the fact that you just bought a pool filter puts you in the narrow group of people who would potentially have need for another pool filter. Even though you just bought one, you're still more likely to be a customer than a random person. Hence, generally speaking, sending you ads for the same thing you just bought may be a rational choice for the advertiser.