A high trust society reduces the incidence of scams/becoming victims to scams by reducing the number of scammers and increasing the number of honest people and honest behavior. That's what a high trust society is and does by definition.

If you want "mechanics", that would be an increased focus on community, with positive community best-behavior incentives (reputation, pride in work, solidarity, rewarding good behavior) and negative ones (shame, ostracism, punishing bad actors), social cohesion, and an emphasis on duty and morality, while reducing cynicism, and selfish individualism. This includes the appropriate role models and media/entertainment landscape.

> A high trust society reduces the incidence of scams/becoming victims to scams by reducing the number of scammers and increasing the number of honest people and honest behavior.

Considering that the scammers in this instance haven't been identified, there's a good possibility that the phone scammers belong to an out-group (e.g. infamous Indian/Nigerian scammers) of the victim's society. In fact, it seems to me that trusting more (because the in-group are honest) without appropriate safeguards preventing out-group members from impersonating in-group members exacerbates the problem. So I do not really see the connection between your solution and the problem.