No one can verify that people aren’t scammers.
Bonded users (shield badge) put real XMR at risk: if they scam and lose a dispute, they can lose the bond. Bonds guide: https://xmrbazaar.com/bonds-guide/

Yellow check / verified users are either well-known in the Monero / XmrBazaar community and/or have a solid prior track record.

Escrow (or a bond) is the only truly scam-proof signal we have: scammers do not lock their own money in 2-of-3 multisig, and they definitely don’t use bonds: it would bankrupt their entire “business model.”

TL;DR: Use multisig escrow or a bonded seller. Always.