Good question. As someone who's been in the business for over a decade and now runs a company that ONLY does 1-on-1 private tutoring, I'll offer the following:
First, literally anyone can say they're an MCAT tutor. All you have to do is hang up some fliers, post some craigslist ads and then convince people to give you money. Voila, you're a tutor.
You can often find people claiming to offer MCAT tutoring who haven't even taken the MCAT. This is especially the case on/near big college campuses. Some physics masters student will look to make a few extra bucks by offering "MCAT Physics Help" even though she's never actually taken the MCAT.
Having said that, there rule of thumb tends to be that to reasonably be able to claim expertise on a section of the test you should be 12+. So if you're going to offer your services as a Physical Sciences section tutor, you should be able to score 12+ on PS. If you're going to be claiming expertise as an MCAT generalist who can help on all aspects of the test, you'll want 33+ in less competitive markets and 35-36+ in competitive markets (large urban areas with lots of demanding clients).
Finally, and most importantly, remember that teaching is itself a distinct skill that can be taught and that some people have a real knack for. When I was working for one of the big companies, the most successful LSAT teacher in the entire state was a guy who only got like 70th %ile on his own LSAT. He was just brilliant in front of a class, though.
So is it possible to be a really good MCAT tutor only having gotten a 30? Sure. But the reality is that you're going to need to be honest with people about your score, and a lot of students will be turned off by that "low" score. One way to get around this problem is to offer your help for free through the college's academic help center (or something like that), and once you've worked with 4-5 students you can get testimonials from them. Convincing people of your teaching ability is a LOT easier once you can show past success. At that point, potential clients are paying you not b/c you did well on the MCAT, but b/c you have a proven track record of success with helping other people on the exam.
Good luck. Teaching is the best way to learn, and you may find after working with a dozen students you could go back and do even more amazing on the real thing (that was certainly the case with me).