it might be helpful to look into the trust model from Mayer and Schoorman.
One possible approach to measure trust:
Dulewicz and Higgs developed a menu-based trustworthiness scale for interpersonal relationships with an item pool to assess trustworthiness in different research contexts (also for a managerial context). The scale measures the four trustworthiness factors: ability, benevolence, integrity and risk avoidance. Dulewicz and Higgs also developed a scale to measure the predisposition to trust (see Ashleigh, Higgs, and Dulewicz).
Since predisposition to trust moderates the relationship between the trustee's (manager) trustworthiness and the trustor's (followers) trust into the trustee you can calculate: trust = trustworthiness x predisposition to trust.
Some references
Ashleigh, M.J., Higgs, M. and Dulewicz, V. (2012). A new propensity to trust scale and its relationship with individual well-being: implications for HRM policies and practices. Human Resource Management Journal, 22(4): 360v376
Mayer, R.C., Davis, J.H. and Schoorman, F.D. (1995). An integrative model of organizational trust. Academy of Management Review, 20(3): 709–734
Schoorman, F.D., Mayer, R.C. and Davis, J.H. (2007). An integrative model of organizational trust: Past, present, and future. Academy of Management Review, 32(2): 344–354
I could imagine that the degree of reciprocity in frequent social relations is also an indicator of trust (just as Granovetter described "strong ties").