Long a great way to unload items from the attic, the garage sale remains one of the bastions of free enterprise in this country. In this sea of junk and trinkets often lie valuable collectible items, marked at lower than bargain basement prices.
As with most things, the first step is education. Obtain a price guide that covers many different collectible items. You can't possibly know everything about every collectible -- the topic is simply too vast. Expect to spend a couple of months with the book doing the exercises listed in the next step.
For each general entry in the price guide, calculate the average value for all items listed in that category. Write these values in a small pocket notebook, next to the collectible category or name. What you are doing by calculating the average value is giving yourself something to compare the asking price of any item in that category. There are more advanced techniques, such as calculating the standard deviations on prices, but average is sufficient for the first year. By doing this exercise, you will gain more knowledge of collectible items than you might think.
One last step before heading out is to make some specialized lists. If you are already a collector of something (most people have something they are interested in), make a wish list of items in your favorite category, whether pottery, record albums or rare old videos.
Plan your garage sale day. Start with the local paper, choosing 20 or so sales around the area you live in. Using a map program, enter the addresses, and plot a map and route. Start along this route, and hit every sale in between: For every advertised sale, there are at least four that are not. Concentrate on neighborhood sales for convenience, and rural sales, which seem to produce a far greater percentage of older items.
Once you are at the sale, immediately start looking at the older items, regardless of what they are. Once you have identified something, discretely check your notebook averages. You can use 10 percent of the average if you are not familiar with the item class. You can usually tell right away from the asking price if the seller knows the item is collectible or not. If you like, use a smart phone to check the selling price on eBay. Doing this will further assist in your collectible knowledge.
One last step before purchase: Do a "common sense" assessment of the item's condition. In the world of collectibles, condition is everything, and the less rare the item, the more it matters. Condition grading is a very deep subject, and varies from item to item and class to class. Don't expect to be an expert; use your common sense.