"Labour," Smith answers, "is the real measure of the exchangeable value of all commodities."
Instead of producing and collecting goods for immediate consumption, local society came more and more into the habit of exchanging corn, cattle, cloth, for money, and of laying money by as a means of getting all sorts of exchangeable goods, when required.
Discontinued boots that are available at bargain prices are less likely to be returnable or even exchangeable, and since the Konas have sizing issues, you may find you have a boot you'll have to sell in turn.
Contact lenses can be quite an investment and are often non-returnable or exchangeable, so you will want to be as sure as you can possibly be before purchasing that you can wear them.
If the camera is a pro or semi-pro camera with exchangeable lenses, reviewers must ask themselves about the lens mount.