Step 1. Click the "Sell" button to become a vendor.

Step 2. Fill in what you wish your customized URL key will be and click submit.

Step 3. After being redirected to your Vendor Panel, choose the Transaction Settings under the Settings option on the left.

Step 4. Set your Paypal email and change "Active" option to Yes. Click save.

Step 5. Choose the "New Product" option on the left.

Step 6. Choose the correct Game/Item Type from the dropdown menu and click continue.

Step 7. Fill out the item/service form and click Save and you're done! Your item is now listed.
Once you've sold your item:
Step 8. Check your Order page within the Vendor Panel.

If it says "Pending Payment", it means the payment has not cleared for one of many reasons.
Step 9. Chat with buyer to arrange sale.
Step 10. Once sale is complete, click "Send Query" to notify the buyer and admin of completion.
Step 11. Wait until buyer confirms the delivery on their end.
Step 12. Wait for Admin to send out payments to vendors (generally twice a day, sales are checked). Profit.