First thing's first, before buying credits from someone check their post count. If they don't have any posts then report them to us. They aren't allowed to sell credits if they have never used our forums.
Next, check their Karma level. You can see their karma on their homepage. If they have negative karma STAY AWAY. Do not buy from them. If they have positive karma then click on the link that says "View comments to user’s karma". This will take you to a page where you can read all of the comments people have left who've given person karma. If the person doesn't have any karma it doesn't necessarily mean they aren't trustworthy. Just means that haven't earned any karma yet. Not many people leave karma for people they buy from unfortunately.
Next, ask the customer questions about what the credits they are selling. How did they earn them, are they stolen, how will you send them to me, how long do I have to wait etc?
Finally, make sure the person is following our rules. For example if they refuse to do business over pm and tell you to go to a third party website or chat service (kik,discord,skype,whatsapp,snapchat etc) then report them to us and do not buy from them. They are allowed to use these other sites and services but they also have to use our pm/billing system too.
Market Rules:
viewtopic.php?f=2&t=8140Frequently Asked Questions:
faq.php