for example:
His name was Otong
Otong is in default trust.
Because default trust He can make a good profit.
Then he make a new account, Gosong.
Then he left his "fake" trust to Gosong has a trust.
Afterward, Otong sell his Gosong's account to other with high value.
Then he create another account and repeat the same way.
Is this possible to happening ?
How can we verify if someone abusing like that way?
If you are dealing with someone with only one source of positive trust then it would probably not be reliable. The person giving the positive trust would also probably be noticed when the source of the positive is always the same when someone ends of scamming others.
Someone could easily do this without an account on default trust. All they would have to do is engage in a lot of trades with users on default trust and with positive trust in order to gain more legit looking trust feedback.
You should always take any trust feedback with a grain of salt when dealing with another user.