As you know, when doing all sorts of transactions that are not face-to-face, you must keep record of every communication you hold with the trusted seller. If the person disappears with your money, create a thread in Nairaland forums to post all the evidence of the user who scammed you, and immediately report it all to the most well-known trusted users and mods of the forums, they will add this user to their lists.
One common technique the scammers have is that after they have escaped with your e-currency they close their accounts and come back with new usernames, however most times the choose to use a name close to their previous one, like Septembr in exchange for September01, this will be a good clue to know if this user was on Nairaland before as a trusted seller, scamming people.
Trusted sellers usually build a thread with proof of their service and demonstrate the reasons why buyers can entrust them with their money, it’s just a matter of investigating beforehand.