Over the last several years radon has become a well known and well publicized real estate related issue. As a result of this trend, testing for radon in homes has become a much more prevalent occurrence. You can include a provision for this test as a part of your overall home inspection. Some home inspectors include a radon test in their inspection (usually at an additional cost). The test takes a minimum of 48 hours for an accurate measurement, so the inspector will usually make some provision for this time frame.
Radon inspectors should be National Radon Proficiency Program (NRPP) certified, or National Radon Safety Board (NSRB) members, or Midwest Universities Radon Consortium (MURC) certified.