Look at the material that the chair is made from. Wicker is woven vines, and therefore a natural product. If the chair is wicker, you will see that it is constructed of woven, interlocking fibers -- somewhat like a knitted jumper.
Touch the fibers with your hand, and gently brush the surface in the same direction as the fibers. Wicker when untreated is slightly rough, but it will feel natural, unlike metal. When it is painted or treated with wax, wicker is smoother but it still retains an organic feel.
Lift the chair if you can. A wicker chair is lighter than durable plastics, wood or metal. See whether you can pick it up on your own.
Hold each arm of the chair, and try to twist the chair slightly. Do not damage the chair when doing this. You are listening for sounds and feeling for movement. A wicker chair sometimes squeaks, and it's possible to move it slightly because of the flexibility of the fibers.
Compare the chair with a picture of a wicker chair. You can find one in a gardening center brochure, for example. Identify similar traits such as the woven fibers, thickset arms and legs, and color. Natural wicker is yellowy before it is painted.
Speak with a friend, or take the chair to a furniture store and seek advice.