You're nearing the end of the selection process. You have spoken to everyone you are interested in at least once, and you are ready to make the choice. Job k nowledge is a function of a candidate's education, training, and experience. Do not be reluctant to ask candidates what they have done, where they did it, and how well they did it. Ask about their successes and the problems they have faced.
Motivation is based on what an employee gets from performing the job.
While salary is important to performance, it is not everything. The best employees are those who enjoy what they do. Your task in hiring is to find people who want and like to do the job for which you are hiring them. Just ask them. You should also ask them what they liked and disliked about previous jobs, and why they want to work for you.