X's OG-username market has existed for close to two decades, so the buying process here is well-established compared to newer platforms — but the same basic care still applies.
Message the seller to confirm the handle's still available, agree on payment, and get the account handed over. Given how established this market is, it's also the one where scam awareness matters most — higher prices attract more attempted fraud.
Open the vault, pick a listed username, and DM the contact handle shown on the site to arrange payment — there's no cart/checkout, it's a direct conversation with the seller.
Crypto-only. See the Terms of Service for the full payment and delivery policy, including the sale-finality and 72-hour issue window.