The best way to test third-party data is to run controlled pilots with clear success metrics and holdout groups. Start with a defined use case, such as prospecting, enrichment, response modeling, or suppression, and compare performance against your baseline or another provider using the same offer, creative, and timing. Measure not only response or conversion, but also match rate, cost per outcome, downstream value, and whether performance holds across channels and segments. For Alliant specifically, testing is often strongest when the data is evaluated on its ability to improve audience quality, predictive lift, or personalization rather than just raw scale.