Most people I know order 3 or more to try and keep the one they like returning the others. Not sure how you can compete on price when people are doing that.
Whether the question is returns or something else. Few will open their wallet if they have doubt. Unlimited and free returns removed a large amount of doubt. If fact, as mentioned, it likely triggered more sales.
You'd have to spend a significant amount of marketing budget to get what Zappos did from their return policy and customer service. Those weren't expenses, they were investments.
That's why Zappos doesn't compete on price, I've never seen a shoe there listed at anything but MSRP. I still buy all my shoes there because I'm very picky about fit, so I order several pairs, wear them around the house, and then pick what I'm keeping and send the rest back.