People who want to attend a particular vocational or trade school should obtain information about the institution's accreditation -- it is simply a form of academic quality control. State agencies, such as the state of California's Department of Consumer Affairs Bureau for Private Postsecondary Education, keep records as to which vocational or trade schools (in their respective areas) maintain that standard -- a condition legislators often mandate by law, according to the Private Postsecondary Act of 2009, for example. Each state most likely has a similar representative body that outlines how schools must maintain "instructional quality" or "institutional stability."
The U.S. Department of Education and the Association of Career and Technical Education have online directories you can use to check the status of virtually any of the numerous vocational or trade schools nationwide. You can also check with various other organizations, such as the National Association of Independent Colleges and Universities. This organization also outlines quality standards applicable to distance learning facilities as well.
Many technical or trade schools have associations that loosely represent them in some form or fashion. You can find information about veterinary technical schools via the American Veterinary Medical Association, for example. The American Association of Design Drafting, Electronics Technicians Association and even the National Automotive Technicians Association most likely have details about vocational or trade school testing or certification requirements.
The U.S. Department of Labor's Occupational Outlook Handbook details vocational or trade school requirements for multiple trade, vocational or technical professions -- educational requirements for health-related occupations such as medical or nursing assistants, for example. The Accrediting Bureau of Health Education Schools, the Commission on Accreditation of Allied Health Education Programs and the Commission on Dental Accreditation all have directories of accredited vocational or trade schools as well.