Basically flagged account means that you cannot recover your account no matter how many info you gave z8games(through the ticket system) because you were either selling or sharing account. However, this benefits the buyer if the seller sold it to him.
Non-flagged accounts are account that can be recoverable. So becareful when you buy an account that is not flagged unless you know this person can be trusted. Remember, no one can be trusted no matter how many post or vouch they get. The newly registered mpgh member are even less trustful.
I was a bit nonchalant when I do trade because of how much I wanted the account, and therefore I learned my lesson...