Power BI consultant ensure seamless integration of multiple data sources by using Power Query to clean and transform data uniformly. They create a robust data model that supports relationships between datasets while maintaining performance efficiency. Consultants apply common data governance standards to ensure data integrity and consistency across sources. By scheduling data refreshes appropriately, they keep reports up to date without overloading the system. Using tools like Azure Data Factory or integration services can also enhance the process of connecting to multiple data sources.