Take a walk through some of the online furniture sites in order to help to train yourself to know various styles and to recognize antiques in any setting. It's relatively easy to know if an antiques store has antique furniture cabinets. That's what is supposed to be there and chances are there won't be many reproduction pieces.
The real trick will be to spot that at the garage or home auction or the yard sale where someone is simply trying to get rid of grandma's ancient furniture in order to bring in something a bit more modern and interesting.
The designs of antique furniture cabinets will vary according to the period in which they were made. Likewise, the materials will quite likely be unique and not often seen. The Oaks, Cherry, Pine or Mahogany woods that you're going to find in antiques are simply not found in the new furniture of today in most cases. Even the most costly modern furniture will have a great deal of veneer as opposed to a lot of solid woods.
Although it is sometimes hard to determine if the piece is a real one, you can learn a bit more by studying books and online sites which will help you to find out more about the various styles and the pieces that might be associated with them. The various time spans, such as Pre-Victorian, Victorian, Early American, American, English, or European will all have their own specific finish, their own styles.
Each item may also have a maker's mark that you can find if you know where to look. Some will be beneath the chairs and in various places. While many won't have those marks, some will give you good clues about the time period and the place that the item was made.