To gain trust, a sportsbook must be trusted and can provide unique services which have licenses and certificates. As well as having cooperation with international agents to provide the most complete sportsbook services.
Have you ever heard about 1xbit? I think 1xbit fulfill your criteria (especially about license) to be trusted sportbook, but what is the fact? They are not trusted at all. Licenses is not a guarantee to be trusted gambling site, most early crypto casinos had no license but they can get good reputation because they can prove themselves that they are reliable and worth to trust.
Indeed. A casino that has a license doesnt necessarily mean they're trusted ( just like what you have said about 1xbit). Thus a license should not only the basis to say a sportsbook/casino is trusted. It takes time to establish a good reputation and it depends on the gamblers how they will trust the specific platform. There are many factors to consider and I think on top of that is the security and how fast the withdrawal is, because often thats the main concern of gamblers.