In our book, "The Complete Money Saver's Guide to Garage Sale Shopping", we talk about the importance of knowing things of value when you see them. You need to familiarize yourself with labels...on collectibles, china, furniture, etc.
One example of this is a recent garage sale purchase we made for $4. It's a large rabbit made by Annalee. The Annalee brand has been around since the 1950's and they are highly collectible. Visit their site and you'll easily spot these very unique pieces when you see them, easy to identify not just by the tag, but by the painted faces. http://www.annalee.com/
The Annalee doll we purchased for $4 would probably sell for about $50 based on comparable eBay listings, and is from the 1960's as dated on the tag. This is a great resale item or gift for anyone you may know that collects them.
Enjoy the weekend!