There are many things to look for in finding a “diamond in the rough” piece of furniture from an estate sale, garage sale or thrift store. Look for the potential in a piece of furniture. This can be broken down into a few categories.
First is function, will it work for you in the way that you are hoping for? If you need a good writing surface /desk, don’t buy something that is too small or too tall or has a warped top just because it is cool: it is important that it fits you and your needs.
Second thing to think about is size. Is the piece going to fit through doors and up the stairs? Measure, measure, measure: if you go out thrifting, bring a tape measure and a quick drawing of the room you are looking to fill, along with some basic measurements. Sometimes (as in a garage sale situation) you need to be quick on the draw, as most people don’t like holding bargains while you go home to measure.
Make sure the piece has good "bones." Look for good structure, how well it is built, how heavy it is, does it wobble when you touch it? Use a little common sense. If it’s falling over, it might be too big a project (although if one leg is loose, a trip to the hardware store might resolve the problem). Also, reupholstering a basic dining chair can be learned from a book in an afternoon, but doing a whole sofa takes a lot of practice and sewing skills.
Lastly does the piece have good lines? Meaning is it architecturally interesting and does it have proportional qualities from an aesthetic point of view (the bowed legs on our piece caught our eye)? If the piece is “close to cool,” you might be able to alter it into a gem by adding appliques or trim, lengthening or shortening the legs, etc. As a rule, if there isn’t something that initially draws you to the piece, it’s probably not a winner.