There are a lot of things that are hard to communicate in ads because they are things that can't really be measured. You might want to look at using customers in your ads to have them talk for you about why other companies should trust you. Testimonials and other forms of social proof are a useful, so long as they are genuine. Build transparency and humanity into all you do - for example, you can clearly outline your returns policy on your website, or answer customer questions honestly and compassionately on social media.
Look for ways you can concretely demonstrate your trustworthiness. How do you prove it? If you can demonstrate that you have a solid product/service, it will be more powerful than saying "Trust us on this one."