For me, it's being reachable.
As I help nonprofits grow their monthly donations, I work very closely with organizations and their missions, waiting days between changes and improvements can cost NPO tons of money in donations. So, when my clients reach out, they hear back from me, usually within 24 hours.
This matter a lot to me, because the nonprofits I work with are stewarding donor money and donor trust. When their gala date changes, or a campaign isn't converting, or they just have a question about their Google Ad Grant, they can't afford to sit there wondering if what we are doing is actually working. Silence costs donations.
One of my clients, Lisa, put it best. She said she looks for vendors she can actually get on the phone, who have the temperance to help her understand what's happening. My clients aren't marketing experts, and they shouldn't have to be. My job is to explain things clearly, respond quickly, and make them feel like they have a partner.