contractor's stability; contractor's flexibility; and contractor's domination. In the next step, due to the theoretical coding, these categories were assigned to the contractor with regard to the employer's trust, and thus, the conceptual model of this research, which included nine case studies, was achieved The results of the research show that some of the results obtained by this research, such as contractor's domination, are due to the distinctive background characteristics of the present study, and some other categories such as contractor's ability, Is in line with the results of past literature; however, the main concepts of these categories were unique and specific in the context of this research. Also, comparative analyzes between government and private contractors in the field of reliability showed that, from some aspects such as contractor flexibility, government contractors were more reliable, and from the perspective of some other categories such as the ability of contractors, private contractors were more reliable than public contractors.