Professionally, an interpreter is not supposed to have tattoos or piercings (other than small, nondistracting earrings) in visible places. Of course, different clients have different thresholds of tolerance, and some deaf clients may tolerate interpreters having open, visible tattoos and earrings. The company I work for now, many employees have tattoos and piercings in all sorts of places (tongue, lips, eyebrow, nose, multiple ear piercings, etc... untypical for an Utahn company!) so that sort of interpreter would not stand out in a company like the one I work for. However, it is a good idea to be prudent with tattoos, placing them in places where they can be covered up in comfortable clothings, and to keep piercings to a minimum. I once had a male interpreter who had thick, heavy metal loops, soul patch on chin and a tattoo on the backside of his arm. It didn't really distract me. I like having interpreters who has their own individuality and personality, but again, not all deaf clients are like me.
Liebling, it is impossible to have an interpreter with 100% perfection. I'd trade in for an interpreter who can laugh at his/own misunderstandings with me than a perfect, übermensch interpreter with no sense of humour.