|I've spent a fair amount of money at Zappos recently, and I think I understand why they're successful. For the uninitiated, they're big on customer service, and specifically on the idea of free shipping and free returns. The thing that sets them apart from other retailers is that second part, the free returns. As far as I know, they do free returns for everything, no matter what, probably as long as you don't destroy it before you send it back.
From an end user perspective, it makes it feel like you're getting away with something. You can buy $1000 worth of shoes, clothes, and whatnot, and you have the option of sending all of it back, at no cost to you. And knowing you'll be able to do this, it makes it seem like you're getting something for free. If you choose to return everything you buy, you're essentially getting free try-ons via mail order. It's a small benefit, but it's something. But the psychological component of knowing you're getting a small benefit is mildly rewarding. Hard to quantify, but there.
I've been thinking about how a business can run this way and still make money, and I've come to the conclusion that it must be working, because otherwise they wouldn't be around anymore. The money they make from people keeping things must surely be more than the money they spend for one- and two-way shipping.