Check for a label. This determines whether the rug was machine made or hand woven. Hand woven rugs rarely have labels while machine made rugs often do. Machine-made rugs' value depreciates over time and costs significantly less per square foot. Hand woven rugs can cost a great deal more per square foot.
Examine the back. If there is no label and you are unsure if it was machine or hand made, you can tell by looking at the back of the rug. Hand made rugs are hand knotted. Machine made rugs have white threads, or "warps" running evenly across the length of the rug.
Know the country of origin. Rugs from Iran are more valuable than rugs from India, Turkey, or China.
Know the date of manufacture. Rugs fall into three historical periods, each with its own value. Rugs made before World War I come from Iran and the Caucuses. These rugs appreciate in value, and if they are in good condition, are worth more money. From between World War I and World War II, rugs tend to be more artistic and this decides their value. Rugs made after World War II have the possibility of originating from India or Pakistan. These rugs depreciate in value and are worth less than their earlier counterparts.