Some species will become very used to people and can be handled carefully without causing stress. Many people prefer not to handle geckos and there are many people that believe you shouldn't, but species such as levis and milii are fine. As long as you keep handling to short periods of time, do it late in the arvo to avoid throwing out their sleeping pattern and monitor their behaviour and food intake which can give you an indication of stress, then you should be fine. Levis is the best option for handling.