Lead validation is the process of separating sales leads from other types of conversions generated by internet marketing campaigns. The author discusses the importance of lead validation for understanding campaign effectiveness and calculating accurate costs. Analysis of over 350,000 inquiries from the past 18 years revealed that around 50% were not actual sales leads. Without validation, campaigns may be optimized using inaccurate data that overstates results by 50%, wasting resources. Lead validation is necessary for improving campaigns and maximizing returns on marketing investments.