In judgement sampling, the researcher or some other "expert" uses his/her judgement in selecting the units from the population for study based on the population’s parameters.
This type of sampling technique might be the most appropriate if the population to be studied is difficult to locate or if some members are thought to be better (more knowledgeable, more willing, etc.) than others to interview. This determination is often made on the advice and with the assistance of the client. For instance, if you wanted to interview incentive travel organizers within a specific industry to determine their needs or destination preferences, you might find that not only are there relatively few, they are also extremely busy and may well be reluctant to take time to talk to you. Relying on the judgement of some knowledgeable experts may be far more productive in identifying potential interviewees than trying to develop a list of the population in order to randomly select a small number.