Avoiding scammers? You can't... They're all over the marketplace in this forum.
All you can do is mitigate the problem... Be VERY paranoid. Insist users send you "validation" PMs from a Bitcointalk account using either signed messages from a staked address or using a unique codeword that you make up on the spot so you can be confident that you're dealing with the correct person and not an imposter.
Don't deal with newbies if possible.
Try and avoid Telegram. Document everything (screenshots of PMs and Telegram where users can unilaterally delete entire conversations at any time!
).
Use Trusted Escrow!... Avoid anyone who refuses to use escrow.
Avoid any "auto buy" deals like selly.gg.
Be wary of users using self-moderated or locked threads that want to deal offsite.
Be very suspicious of extreme discounts (likely stolen, fake or carded)