I own a business and at times have to "eat" some business so to speak, and do it for the benefit of my customer. It's not only the right thing to do, but it pays dividends on the long run. There are times when a customer is asking for something unreasonable and a return/exchange isn't possible but this is just wrong. And I don't give a rat's bladder if it's legal to resell the protective sock or not. Swiss Barefoot Company, just write it off or risk being a second rate customer service company.
I was considering purchasing their product. Given I sometimes need to exchange sizes of footwear products online, not a chance.