Below excerpt from the book Work Less, Make More by James Schramko. He did it for his SEO agency, but many service-based businesses could do similar.
We charged people $20 to look at their website and provide a report on what state it was in, how well it was optimised, and what they should change.
We then said we’d credit the $20 towards any of our recurring SEO services. The diagnostic service was really effective for us, converting more than half the people who bought a report into an ongoing recurring program.
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