Breed, color, luster, crimp, length, cleanliness, and weight are the basics. Knowing if the fleece is skirted or from a coated sheep is helpful as are the age (fleeces change every year of lifespan) and sex (some people object to the gamie smell that a ram fleece has) of the animal it came from. Testing the strength of the fibers is a hands on thing that can only be judged physically, not something that a photo can tell. All these things will dictate the price per pound of wool which is the bottom line.