You can only tag people whom you're friends with via your personal page. I always thought it would be nice if you could tag fans of a business page in photos posted on the business page, but facebook doesn't allow it. What I'll sometimes do is send the client an email with a link to the facebook gallery and say something like "Hey, here are some preview images from your session/wedding/whatever, feel free to tag yourself or your friends if you want the pictures to show up on your/their page." Sometimes they do, sometimes they don't. A couple people have saved the images onto their computer, then reposted them on their personal page - so there's no link back to my website or business page, which is annoying. Bonus points if they pass the photos through an Instagram-style filter, crop out my watermark, then repost the image...