Here is a tip: a reliable marketing agency never lacks data, because it uploads everything that might be useful, and then performs a detailed analysis and report.
Ask about the process of data extraction and analysis in the company. Then find out about the reporting forms that the agency plans to provide. For example, apart from the daily monitoring, we create large weekly and monthly reports to track and show the progress and results of our work to the customer.
Also, be sure to ask the marketing agency to show you their cases. Experienced contractors always have their portfolios ready. But besides the results themselves, make sure you ask a few questions about the project details, because true professionalism is in the detail.