If someone does not want to be interviewed, that's certainly his or her right.
Plenty of people are wary of strangers in general and journalists in particular. Even a public official is not obligated to grant an interview. But if a source is important to your story, here are some tips for enticing him or her to cooperate:
• Don't use the word "interview"—it can be off-putting. Say you'd like to talk or chat. It sounds less intimidating. (But be clear that your conversation will be on camera.)
• Like a good salesperson, try to intuit what's causing the resistance and overcome specific objections by anticipating and accommodating the person's concerns.
• If it's a question of the person not having enough time right then, offer a more convenient time or place—perhaps in the person's car on the way to work.
• If someone is afraid of looking bad or sounding stupid, explain why his or her perspective is so vital and necessary for your story.
• If the person claims to have nothing to say, reiterate the information you are seeking. If he or she still feels uncomfortable, at least ask for suggestions of other possible sources.
• If you're having trouble getting accessto a source, particularly one in an official capacity who may be surrounded by protective underlings, be persistent. Call, write, email, or just show up. Find a mutual acquaintance (or another source) to serve as intermediary.
• Be clear that the story will be told with or without the person's cooperation—and so to be fair, you want to provide an opportunity to tell his or her side of the story.
Appeal to the person's vanity. Each person has something special and important to contribute to your story. Emphasize the person's unique contribution.