Final answer:
For troubleshooting errors reported by the sales representative, Azure Monitor is the best tool because of its comprehensive monitoring capabilities.
Step-by-step explanation:
To troubleshoot the source of and reason for errors reported by a sales representative, the most appropriate tool to use would likely be Azure Monitor. This service provides comprehensive monitoring of applications, infrastructure, and network performance, helping to detect and diagnose issues across different Azure services. It includes features like alerting, telemetry, and analytics that are useful for understanding system behavior and identifying problems.
Other tools such as System diagnostics can be used to gather information on system performance and setup, and the Environment History could provide context on changes made to the environment that might have led to the errors. However, Azure Monitor is specifically designed for the type of comprehensive monitoring and troubleshooting that is likely needed in this situation.