An easy way to accomplish this, without demanding an artist produce live clients, is to attend a tattoo convention and simply ask owners of wonderful tattoos who did their work. Tattooed people are always happy to talk about their tattoos, if the person who is asking has a good attitude and a sincere interest in the art, and will be glad to recommend artists that they are satisfied with. Don't be shy, even if you don't have any tattoos yet. You'll be respected for taking tattooing so seriously. Also take into consideration the type of tattoo you want.
Artists have their specialties, specific styles of tattooing that they excel at and love to do.
Yes, a good tattooist can usually put on any style of tattoo you might desire and do a more than adequate job of it. Some artists love to work in tones of black and gray, others have a wonderful sense of color. Terrific tattoos are born when both artist and client are enthusiastic about the piece. That translates to mean that attitude counts. You have a right to have your important questions answered, and not to feel pressured into settling for a piece that's not quite right for you.