The [W] Market, owned by Cynthia, is one of the town areas where you can buy/sell silver keys, diamonds, mithril, and palladium. You must beat the Terminal to unlock this area.
[R] Coupon Edit
Commodity coupons can provide a number of items, these being the following:
- 2 Metal Scraps
- 2 Raw Hides
- 2 Wood Splints
- Silver Key
- Mysterious Artifact
With the market unlocked, commodity coupons will randomly appear while you explore. They will appear as a separate event, just like the quest items and marketing vouchers. There is no limit as to the amount of coupons you can carry at one time.
* : Augments can indeed be found from commodity coupons, however the chance for receiving one, as with augments in general, is very low.
[Q] Quest Edit
Just like the blacksmith and Gladius, Cynthia will also ask you to collect a unique quest item for her called Cherubii. It will randomly appear while you explore, and bringing this to her will provide you with a random item.
[T] Talk Edit
As with all the town areas, you may talk to the NPC in the area, but it is optional to do so. For the Market, you can talk to Cynthia to learn more about her personality and story.
 to  Buying Items Edit
You will be able to purchase certain items from the market, those being silver keys, diamonds, mithril ore, and palladium ore. The prices and stocks for these will fluctuate periodically, but also scale to your level (as shown by comparing the 1st image on this page to the one shown below). You will normally never need to buy these items, unless you want them to complete the blacksmith's mission, for crafting, obtaining access to arena fights, or for other purposes.
[Z] to [V] Selling Items Edit
Just like purchasing items, you may also sell these same four items. The sale price is slightly lower than the purchase price for these items in order to discourage buying and selling the items at the same time. You can sell as many as you have in your inventory, and there is no fixed gold amount for the vendors that purchase your goods. It is recommended, however that you keep some of your silver keys (~10, minimum of 3) since there are events such as the locked chest that will require silver keys in order to obtain an item or progress through the story.