Before paying an x402 service you have never used, ask whether it works. Kortex answers from evidence: uptime measured over time, whether the endpoint returns a valid 402, and how many distinct wallets have actually paid its address on-chain. Measured across 1,015 listed services, only 25% answer with a payment requirement at all. US$1.00 of prepaid credit, about 200 checks, debited off-chain.