Commerce Permission
 
To get commerce permission, first of all you need to finish a quest:

Quest Name

Low Level Commerce

Requirement

Player Level 20 and above

NPC Location

(801, 3657) at Shaitan City

Trader Sidorf will require you to gather 40 pieces of wood in order to get a Commerce Permit from him.


Note: To obtain wood, learn Woodcutting as a lifeskill or you can purchase from other pirates.

Reward

Low Level Commerce Permit x 1 (Non-tradable)

 
About Commerce Permit
After finishing the quest, You'll get a 30% tax rate Commerce Permit. With this pass you can buy commerce items and sell them, but 30% of your profit will be deducted as tax.
 
If you want to get lower tax rate you will have to do more quests at this Trader Sidorf guy. It can be exchanged to intermediate Commerce Permit with the beginner Commerce Permit tax down at 20%, and can be exchanged to expert Commerce Permit with the intermediate Commerce Permit tax down at 10%.
 
About Item Level
There are 3 diffrent levels of commerce items - low, middle and high, higher level items could be sold for more than lower ones, but if you want to buy/sell higher level items, your commerce permit should reach respective level as well, say, beginner, intermediate and expert.
 
Talk to a trader, and click on "Cargo Trade":
 
You can find the items the trader sells and buys, the red ones are the ones that you can not buy at your commerce permit level: