The important thing to know is the safe working load of the rope.If the rope doesn't specify it's breaking strength or safe working load (SWL), don't buy it, you don't know it's quality. SWL is usually considered 1/5 to 1/6 of the breaking strength and 1/10 if lifting a person. Here is a good link to check;
http://kickinteractive.com/dc/units/1_1/safety.html