Job knowledge is a function of a candidate's education, training and experience. Don't 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've faced. Ask for references and call them. Verify education and training, too.
Motivation is based on what an employee gets from performing the job.
While salary is important to performance, it's not everything. The best employees are those who enjoy what they do. You task in hiring is to find people who want and like to do the job for which you are hiring them. Just ask them. Knowing their hobbies and outside interests can help you in your hiring decision.