Amazon's marketing has a fundamental flaw. It sends you offers about things you've already bought; 
despite the seemingly obvious fact that you already have it.

eg: I bought an SD card from there, so now the automated algorithm thinks my hobby is collecting 
various forms of memory, and keeps sending me crap as if i want to improve my SD card and pen drive 
collection.

If you buy a chest of drawers from IKEA, they'd obviously be better saying "OK, so you have a chest 
of drawers, now what about a bedside table?" instead of "Hmm, ok. You seem like a chest-of-drawers 
enthusiast. Do you want another chest of drawers?"

</rant>