All this information is available free or at low cost. All you need to do is learn how to find the books that will identify and hopefully help set a selling price. Look your item over closely to determine if it is an antique or collectible. On furniture, look at the hardware and nails or screws. Are these things hand made or machine made.
Uniformity is the hallmark of machines.
If you believe that your item is a collectible, no matter what age, someone has written a book about it or included it in a book of similar items. It is time to hit the books. Books on antiques and collectibles come in two varities, reference works and price guides. Reference books are written to aid in identification, establish rarity, and to explain variations that exist in a product. A good reference book will explain why two products that look alike to the untrained eye are indeed different and why one is worth hundreds of dollars and the other is worth fifty dollars.