Nope. Payment details are not required to make an account. Must validate phone number though.
Here - https://gameflip.zendesk.com/hc/en-us/articles/206466117-Account
Not exactly sure what you meant. I assume you meant that they have verified their details and did a few successful purchases/verified account to be Gameflip verified. Depending on how often they buy, the cost of the listing they bought and also whether they give the correct details that Gameflip requires, the time varies.
As I suggested on your other topic as well, you can suggest anything or express your thoughts to Support or DarkKnight/MajorTom via DM.
References -