I don't think "educating" clients about quality is worth the effort. Just deliver code to a quality you are happy with and tell them that it takes as long as it takes (giving them feedback as regularly as you are capable of, so they get a sense of progress).

Good clients will understand and bad clients will filter themselves out quicker (which is a blessing in disguise even if they do sometimes give you money).

I prefer to let cold, hard reality do the teaching.