With all those cash-strapped college students, retirees and moonlighting teachers, there's no dearth of tutor choices. How to find the right one when word of mouth isn't working.

Get a background check.

Unregulated markets like Craigslist may be okay for finding a used couch, but experts caution against answering random tutor ads. Reputable agencies will conduct criminal background checks and consult sex-offender registries. (Online tutor portal WyzAnt lets families purchase a check for $8.) Such measures aren't infallible, since many checks only go back seven years.

Decide how important pedigree is.

Diplomas from elite universities sound promising and make for impressive cocktail party chatter when you're comparing tutors. But they can kick up the ka-ching factor. Advantage Testing, which offers tutoring in a dozen markets for as much as $795 for 50 minutes, says its rates reflect not only its tutors' qualifications, but also its belief that teacher pay should be on par with that of other valued professionals.

Question certifications.

Since states don't regulate tutors or tutoring agencies, it can be hard to know which ones are credible. A handful of industry organizations offer fee-based certification for individual tutors; each requires a minimum number of tutoring hours, along with completion of a training program. Critics say these credentials haven't gotten much traction out in the field: "I've seen many organizations come and go," says Mike Zenanko, who runs a tutor-training center at Jacksonville State University.

Do a trial run.

Good instructors come with all kinds of backgrounds, says Cynthia Neuman, owner of All-Ivy Tutors, a New York City boutique agency. To help determine if a prospect is well-versed in the subject needed, ask for at least two current references, including specific academic results. Experts suggest doing a one-session trial, watching closely for intangibles like patience, empathy, creativity, humor and, of course, chemistry with your kid.

For more: The Tutor Boom, 10 Things Tutoring Services Won't Tell You, 10 Things College-Prep Advisors Won't Tell You.