This is the case for fine jewelry and e.g. diamonds, however, simple heavy gold jewelry (e.g. rings, chains) are generally sold at a minor (10%?) markup over the cost of the metal and would be generally included in the retailer's markup - i.e. buying a 100 gram bar of gold would cost about the same as buying 100 grams of assorted gold jewelry. Fine pieces of art certainly can cost much more, but the local jewelry stores aren't really selling that, they're selling pieces for which almost all of the value is in the material, requiring only limited amounts of inexpensive jeweler's labor. So there's some overhead, but in general it does retain the resale value quite well.