Watch out for third-party sellers. To ensure a valid warranty, it is safest to buy from Amazon.com directly or the official Vitamix storefront.
Known for having some of the best prices on new machines, Costco also offers a "bulletproof" return policy. If you decide the machine isn't for you or it fails outside the official warranty, you can often return it for a full refund.
They offer a 60-day risk-free trial—longer than most retailers—and will even pay for return shipping if you aren't satisfied. Amazon: Best for Prime Members & Major Sales