Best way to test if eco-friendly packaging actually drives purchase decisions?

Conjoint is your best bet here since it forces trade-offs between price, sustainability claims, and other attributes — exposes actual preferences vs. stated ones. We ran a CBC study for a CPG client with ~300 respondents and eco-packaging only mattered when the price premium stayed under 10-15%. Pair it with a small in-store A/B test if you can, because claimed behavior and real basket data still tell different stories.