you have to be an established user. Meaning you need to be apart of the community, you can't just outright start selling credits, you have to earn that trust and due to that I wouldn't buy from anyone who doesn't at least have 5 karma. A few select people have scammed on here so that's another reason why. Also the way you sell credits is
buysell/manage_ad_credits.php?mode=create_ad&step=1but it WILL NOT let you until you become established. So putting this in the forumns kinda goes against the rules..
Noone on here knows you
You have 0 trust because you're a new user
Selling through forums is a no-no. for things to be done properly it has to be put in the system, and someone has to legit order from you so that no-one can be scammed and if it is then everyone will know you're a scammer and never buy from you again.