Final answer:
The most common reason for difficulties during the interaction of customers and contact personnel is unreasonable demands. A lack of attention to detail by contact personnel can also contribute to difficulties.
Step-by-step explanation:
The most common reason for difficulties during the interaction of customers and contact personnel is A) Unreasonable demands. Customers may have unreasonable expectations or requests that are difficult for contact personnel to fulfill.
In some cases, d) A lack of attention to detail by contact personnel can also contribute to difficulties. Contact personnel may make mistakes or overlook important details, leading to customer dissatisfaction.
However, it's important to note that the other options, such as b) A technical breakdown in service delivery or c) Incompetent contact personnel, could also be contributing factors in certain situations, but they may not be as commonly encountered as unreasonable demands and lack of attention to detail.