In fact, he does, that's one of the most important characteristics of Mihawk. He's able to evaluate people.
He was able to see Zoro's will, determination and potential back in Baratie.
During Marineford, he tested Luffy, and said that even tho he isn't as strong now, his greatest power was how he could make people around him turn into allies.
He also tried to evaluate Whitebeards power, but Jozu interfered.
Mihawk is very observant, in fact he was suposed to be called The Clairvoyant.