The process works like this:

1. You place items you want to buy in a wishlist at amazon
2. You hand this over to purse along with btc and the price you are willing to pay in btc in (purse broker and escrow in one)
3. Someone that accept the price then buys the wish list which whatever funds they have (they don't know who u are or where this goes, they just pay for it and amazon handles the shipping etc).
   They usually do this because they have amazon credit (such as gift card or worked for amazon) that they need to liquidate.
4. Amazon ships the package
5. Once you received the package you confirm delivery and the btc gets transferred. You have saved money and the the buyer has liquidated their amazon coins for btc

If at any point there is an issue purse steps in and makes sure everything is handled correctly.

IF you need to return your stuff, it works the same way as any other amazon shipment.

I have not tried to buy something 20% off and return it for a 100% refund.