Snapchat has historically been stricter than most platforms about letting users change their username after signup. That friction cuts both ways for the market: fewer short handles churn back onto the open market, but the ones that do tend to have been held — and used — for a long time.
Because changing a Snapchat username isn't as casual a decision as on, say, Instagram, a short handle up for sale is more likely to represent a deliberate account transfer than someone simply freeing up a name they got bored of. That tends to mean fewer, more considered listings rather than a constantly churning inventory.
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.