Welcome Etone!!!!
With buying, selling, trading there are always risks involved. Seems like trading is the highest risk on this forum.
On selling- give full disclosure on the item to sell, good pics, and be willing to bite your tongue if someone asks for a refund. Not everyone agrees to what's described, yes even with pics. Make sure you
package your items securely and take pics. Always provide a tracking number and a signature requirement, it helps protect the seller.
On buying- if you commit to buy something, then buy it. Don't ever use PP family/friends option even if it means you won't get the item.
On trading- Go look up the person you want to do a trade with. See where that person does most of his posting, you'll get the hang of who's a contributing member and who flips knives by
looking at their post areas. Feedback scores are a good indication, but don't solely rely on the feedback system.
Read,read,read the GB&U forum frequently, it's where you'll learn the true colors of people. The ignore feature is your friend.