We use five tiers because they solve three problems a marketplace must solve simultaneously: trust, scalability, and behavior change.

First, a tiered ladder is materially more credible than a binary “eco / not eco” label. Binary systems invite greenwashing because the incentives push hosts to self-label with minimal effort. Five tiers lets us communicate progress and nuance: a home can be meaningfully cleaner and safer without pretending it’s the “best in class.”

Second, five tiers supports scalable operations. We can onboard broad supply at Wood/Bronze/Silver with straightforward self-attestation and targeted evidence, while concentrating heavier verification and spot audits on Gold and Diamond, where trust expectations and brand impact are highest. That keeps platform ops efficient without weakening the integrity of the top tiers.

Third, five tiers drives continuous improvement. Hosts climb ladders when the next rung feels attainable. If we compress to three tiers, the jump becomes too large, hosts stall, and we lose the core mechanism that encourages upgrades over time. With five tiers, we can clearly define “baseline eligibility,” “meaningful progress,” “strong consistency,” “verified excellence,” and “best-in-class stewardship,” without diluting Diamond.

In short: we don’t use five tiers merely for complexity, but rather, it creates the minimum structure that protects brand integrity, keeps verification feasible, and keeps hosts moving upward.