If it's an "expensive" product, you ask people to buy your product and have them send it back to you for a reward. If it's cheap, the reviewer can keep the item in exchange for a desirable review. The sample rate is irrelevant.. you just need enough reviews to out rank your competitors.

I'm not in the industry but I'm willing to bet there are flourishing communities that participate in this type of trade. And it's as sophisticated as it needs to be to get around Amazons countermeasures.

How else are we seeing so many corrupt reviews? Not like Amazon is just passively watching this happen. This is a huge issue for them since it's a bad user experience and Jeff Bezos is obsessed with satisfying customers.