I predict that you could make a living from garage sales, yard sales, moving sales, and estate sales, as follows:
Every week, consult local newspapers and websites to find the upcoming garage, yard, moving, and estate sales. Especially note those in middle- to upper-class older neighborhoods. Why older? Because their residents are more likely to have been there for years and thus have more good stuff to sell. Use maps.google.com to print out a map of the area, and put an X on the locations of all the sales you plan to visit.
On the first morning of the sale, plan to arrive at your first stop at least 15 minutes before its scheduled start time. Bring your iPhone or other wireless internet device with you so you can check ebay.com to see what similar items sold for.
Generally, the professionally run sales are the worst for you because they charge high prices. If you see a professional sign, skip it or come back 1/2 hour before the sale ends--at that point, they may be willing to give you a real bargain. In any event, you must be a tough negotiator or you probably won't make enough money to make this endeavor worth your while.
To take advantage of auction fever, sell your lightweight items (jewelry, collectables, etc) on ebay. Sell heavier items, for example, furniture, at a consignment store, on craigslist.com, or a publication read by people likely to buy the product you're selling.
Keep track of what sort of products are yielding you the highest net profit and focus subsequent treasure hunts on those items.