We need a high trust society.
Everything else is band aids on a broken one.
Everything else is band aids on a broken one.
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.
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.