Identifying avocado takes some skill and may not be possible without touching and smelling. I had an assorment of unidentified grafted trees and have been learning about them. The variables are fruit size, shape, color and texture of skin, and season, leaf size, shape, color, and scent. Then there is the possibility of having an unnamed seedling. To really identify you need someone familiar with the tree as it grows in your area and able to assess the listed variables. Even then I've seen differences of opinion between knowledgeable persons. Some of the common varieties are pretty easy though.