Credit/No Credit
Unfortunately, the course credit is the handiest way of "measuring", along with GPA, academic success, and employers frequently use them as the measure of knowledge possessed by a job candidate, particularly in the absence of significant work experience.
In an interview situation it may be possible to speak to your knowledge in the absence of degrees, credits, GPA, but pre-interview screening of applications may not allow you to get to an interview. Perhaps instead of free, charge some modest fee that would result in some alternate measures that employers would value (course completion time, average score on exams, access to papers written, etc.) would provide employers with useful information. Once a number of applicants listed such on applications, it would tend to increase the acceptability.
