You'll have to define what a "tiny number" means in this context, but I've certainly returned a bunch of stuff to Amazon over the years that I've been a customer, and they haven't cut me -- or anyone I know personally -- off yet.
Their return policy is decent but not particularly generous or anything: if you return something that's not defective, you have to pay the freight back to them, and they have to receive it before they issue you the credit. I suspect their return rate is fairly low compared to retailers with more generous policies (e.g. Zappos, REI, LL Bean, etc.).
Thats different within the EU. If you return it within 14 days and its worth more than 40EUR Amazon has to pay for shipping. Its called "Distance Selling Act" (Fernabsatzgesetz in Germany). It applies to all non digital goods sold online except Software and Music.
