Consultants prioritize data validation by thoroughly auditing source data for inconsistencies before integration. They use Power Query to cleanse and transform data while maintaining traceability. Data modeling techniques like defining proper relationships and using calculated columns carefully ensure accuracy. Power BI consulting services implement error-checking DAX formulas and create test scenarios to validate outputs. They also establish clear communication with clients to understand data requirements, reducing misinterpretations and ensuring the final solution aligns with business objectives.