It depends on different things and for different gamblers different things matter. First of all you need to work without problems and show good results in troubleshooting. Also you need a thread with feedback from the gamblers.
Promotion campaigns are sort of advertisement and can not be considered as what you can think of their trust level. A scam casino or exchange can run very attractive, well-paid campaigns but later they can make scam exit.
You`re right, but this is the way to get new gamblers faster and to get feedback. New casino without promotion can`t get trust - no one know about it, no one gamble their. And the bounty manager name can add trust to. If he is trusted, he usually do research and don`t want to work with scam. So i think that it is a part of getting trust too.