Product Sampling is ostensibly a convenience -- you can try items you'd otherwise never consider. However, it also serves as a physical reminder of Amazon's far-reaching data collection. Even if you're fully aware that Amazon has a detailed record of your purchase history, it could still be creepy to receive cat food or moisturizer without asking for it.

There's also the question of whether or not partners get their money's worth. Participating companies have to pay $2 per sample on top of the costs of the samples themselves, and there's no guarantee that cost will translate to more sales. It might just be more practical to lean on conventional advertising and retail samples than to ship goods and hope for the best.