Research probably isn't high on your list of things you love to do. If you're still in or recently out of the school system, you know it's something teachers and professors alike prescribe as torture. But when it comes to garage saling, research can really help you in the long run, and there are valid reasons for sitting down at a computer and looking up some of the items you're interested.
This process works best if you already know what you're looking for, and garage sales are just a means to get it cheaper. A note: it's nigh impossible to find exactly a specific brand and model, unless you're talking about a toy that was popular ten years ago and now everyone is getting rid of, so you're best off knowing generally what you want and letting the garage sales determine the specifics. For instance, a couch -- you may know what size you want, but as far as number of cushions, color of the fabric, and type of materials, you probably can't afford to be too picky if you're going to buy it from a garage sale.
Where are the best places to start your research? Anything online that resembles a garage sale, such as eBay, are great spots to begin your hunt. Here you'll find items starting at the lowest possible price (some have reserves, of course) that the owner is willing to sell them for, and also bids all the way up to how high some shoppers are willing to pay for them. This is very useful information because it gives you a good target range for your own shopping excursions.
Craigslist is also a great resource. Here, you'll find locals who are trying to quickly pawn off their items for some cold hard cash, which means the prices are often steeply discounted from eBay and certainly from retail stores. There's also the free section, where you can find unusual and normally expensive treasures from people moving and desperate to be rid of their items. Craigslist gives you an idea of the going rate for items that someone is really looking to hand off on you.
For newer items, department stores tend to have the most reasonable prices in the world of retail. If the item or items you're on the hunt for are newer, you might want to snag a copy of your local department store ad paper, which will give you some sense of the current market value of items (instead of, say, eBay, where much of the stuff is used or older).
So why else is research so useful? It can give you a bargaining chip with hosts who might otherwise try to rip you off or sell something to you at a high price. You can tell a host that you've seen the item for X amount of dollars elsewhere and that you would be perfectly happy to buy it from eBay, Craigslist, or your local department store. Often, the thought of losing the sale altogether will make the host drop his or her asking price to something you're willing to pay.
If you know the shipping costs vs. the price of being able to pick it up now, this helps you determine if the difference in price between the garage sale and the online bargain is worth it. Big items cost vast amounts of money to ship, sometimes even more than you paid for the thing itself, so being able to drive away that day with your purchase in tow may be financially more sound and just more satisfying all around.
More research awaits you at GarageSaleCow.com, where you can find garage sale listings in your area for free!