How to Effectively Promote/Market a Product Post-Launch?

I recently launched AutoVerify.co.uk, a service that provides instant vehicle history checks for buyers and sellers in the UK. It helps people verify a car’s history—including outstanding finance, previous write-offs, and more—before making a purchase.

I’d love to get insights from the community on the best ways to promote a product like this. My goal is to reach car buyers, sellers, and dealerships while keeping marketing efforts cost-effective.

For those who have successfully launched and marketed similar services:

What strategies worked best for you? Any niche communities or platforms that proved effective? How do you balance organic growth with paid marketing? Any mistakes to avoid when promoting a trust-based service? If you’ve launched a B2C service, especially in the automotive space, I’d really appreciate your insights. Thanks!