Use when an agent is about to pay an x402 endpoint, seller domain or wallet it has not used before. Returns ok_to_pay, caution, dont_pay or no_payment_needed with reasons: live payment terms, its Coinbase Bazaar listing and paying wallets in 30 days, whether the live pay-to address matches the listing, real-USDC check, price vs. similar tools, and seller domain age. Read-only: never pays or signs.