Look at the lines of the sofa. Gently rounded sleigh arms meet at the sofa's back and curve down to the seating area. A straight back goes into gracious curves to meet the arms. Empire styling is prominent in the sofas created by Duncan Phyfe. There is a definite fluid motion to the design.
Study the claw feet and wood trim. For the most part, Duncan Phyfe worked with rich mahogany embellished with plenty of hand carved detailing. A good reproduction should not look like it is mass produced. In addition, it should have a definitely aged look that you would find in a piece still in existence from the early 1800s.
Inspect the brass studs or nail-head trim around the wood trim. A good reproduction will have antique-looking brass studs or nail-head trim solidly spaced at all points where upholstery meets wood.
Examine the upholstery. Original Duncan Phyfe sofas were not overstuffed. Stripes were popular. At times, leather and fabric were mixed. If leather upholstery, you will notice very little piecing. A Duncan Phyfe sofa on display at the Metropolitan Museum has a cane back and feet which are a departure from most Duncan Phyfe sofas.
Find rolled accent pillows to place alongside the arms. Many original Duncan Phyfe sofas came with matching or coordinating upholstered accent pillows. Often Duncan Phyfe-style sofas are sold with an array of accent pillows.
Review the dimensions of the piece you are considering. While there are variables, 34 inches by 84.75 inches by 23.75 inches is a good average size for a Duncan Phyfe-style sofa.