Your credibility is only as good as what your Clients say about you.
So make collecting “Testimonials”(without resorting to strong measures) a key part of your business.
Ask them for a testimonial one week after the Business has concluded. And then send them another reminder a month down the line and so forth.
These regular nonthreatening reminders are very important as most folks are so preoccupied with “life” that they rarely take the time to write a good testimonial, even if you saved their Business from a fire-breathing Koala.
But, if someone’s not gotten back to you with a testimonial after fifty years, despite all the reminders, it’s safe to assume that they probably never will.