Accreditation. Is the institution regionally accredited? If in doubt, contact the Department of Higher Education. Is the program that you're interested in accredited by the major disciplinary body in your field? For example, if a clinical psychology program, is it accredited by the American Psychological Association? Note that not all disciplines accredit programs. Do your homework
Beware of any degree that is offered based on your work history or seems to be very easy to take very little time. If it sounds too good to be true, it probably is.