The proof is in the fabric.
When buying a dining room table or a bedroom suit it is relatively easy to determine the quality of the furniture by looking at how it is constructed. How do you determine the quality of upholstered furniture when much of the construction is hidden under fabric?
First start with the fabric, it is the easiest to evaluate because you can see and feel it. Sofa upholstery is very similar to sheets, the higher the thread-count the higher the quality. The easiest way to evaluate the quality of a fabric on a couch or sofa, is to feel the thickness of the fabric.