Comment by cjg

Giving refunds isn't sufficient.

The reason why trades happen is that both sides value what the other party has more. So I value a book more than I value the money the seller wants to charge for it, so I buy it.

So that means that I would lose out with a unilateral unwinding of the trade.

Imagine the outcry if this happened in the financial world: "Yeah, we sold you that stock, but we're taking it back now, you'll be OK because we're giving you the money back." Isn't going to fly.