Without being in the antique and estate business, it is very difficult to know if you have something of rare value, or just something that’s old.
There are so many determining factors.
For example, a lot of mid-century Danish furniture may be authentic, made in Denmark, or it may be a copy. There’s a big difference in value and probable selling price.
Also, tastes change. A few years ago, furniture built in America during the 1950’s to 1960’s was simply old furniture. Now it’s starting to become “chic” to have “mid-century” furniture and this furniture can sometimes fetch a premium at a sale.
Again, it is best to have the services of a professional who deals in furniture and antiques every day to help you make the best estimations.