A middleman is a trusted third party who holds payment (or the account itself) in the middle of a deal, releasing each side only once both parties have delivered their part — a way for two strangers to trade without either one having to go first and just trust the other.
It's a long-standing practice in peer-to-peer trading communities generally, not something specific to any one marketplace — the underlying problem (neither side wants to go first) is the same one escrow services solve more formally elsewhere.
Deals go direct between buyer and seller — see our Terms of Service for the full payment and delivery policy.
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.