Great!! I love to go to yard/garage sales, too. Some of my better purchases include diamonds—in particular an old european cut around 3/4 carats, rubies, emeralds, sapphires, 14k and 18k bracelets, and lots of sterling silver jewelry, all very cheap. I buy it either to wear or scrap, so broken or whole, it does not matter. One does need to know the european gold and silver markings.
In short, Saturday mornings are treasure hunts for me.
Wow! You must live in a pretty high-end area! I occasionally find some gold, but it’s mostly sterling which I clean up and slap on eBay. I find better luck with gold and gemstones at local auctions.
I once bought at auction a box lot of “costume” jewelry which contained a gorgeous Mexican sterling and amethyst bracelet and earrings (sold it at a Skinner auction for a very large sum), a lapis and 14K gold bead necklace, and about $2K worth of other non-costume jewelry. I paid $90 for the whole thing, picked through it, and then sold the remainder on eBay for $75. One of my best experiences!