Treat it as high-risk. When a seller (or buyer) pushes you off the marketplace to WhatsApp and asks for a bank transfer, gift card, or a “deposit to hold the item”, you lose every buyer protection. That's the point.
Hi, the item is still available! I have other buyers, so verify your details and send a 20% deposit within 24 hours to hold it: market-hold.examplenot Whatsapp's real domain (whatsapp.com). We can continue on WhatsApp.
Illustrative example of the pattern, not a real message someone received.
How to verify it yourself
Keep the whole deal inside the platform, chat, payment, everything.
Never pay a deposit by bank transfer or gift card to a stranger.
“Other buyers, act now” urgency is a pressure tactic.
Reverse-image-search the listing photos, scam listings reuse stock images.