To measure the return on investment (ROI) of the purchased list of prospects, the consultant should recommend importing the list as new Leads and mapping the Campaign during import. By associating the leads with a specific campaign, Cloud Kicks can track the effectiveness of the purchased list and measure ROI through campaign reports. This approach allows sales reps to contact the leads and enables the organization to analyze the performance of the campaign linked to the purchased leads. Salesforce's campaign management and lead tracking features support detailed ROI analysis and reporting.