There is really only one way to earning lots of Gold in the game: selling stuff (you can, of course, live off what you farm/train, but it doesn't get you too far). However, implies that you have something to sell in the first place, which leads us to:

Step 1: Searching for itemsEdit

Depending on your level and the equipment you sport, there will be different kinds of monsters you can best in effort to find items worth selling. Therefore, rather than saying you should be at a specific place at a specific level, I will specify what monsters drop interesting items. I choose the first map, since this is a guide for newcomers, but I might expand it later.
Woody-Wordy Forest / Woody-Weedy Forest:
In here there are four different monsters, one mini-boss and two boss-type monsters. If you can survive a showdown with the bosses, you may find a Bulldozer Cloak, an extremely rare cloak which offers the used two armor points. These two also drop rare skill books and a bag.
Howver, if you aren't able to kill BULLDOZER or his/her brother or need something to do while waiting for them to spawn, the other monsters in this map also give nice items:
Kooii, the lowest leveled monster in the game (besides Young Kooii in the Training Grounds) drops a lot of different items. The four worth mentioning are those: Cloth Robe*, Armor Enchant Scroll (D Class) and Kooii Card 10. Among those, the enchant scroll is the one worth the most, however also one of the rarest.
The next monster is Bramble Donguri, a weak monster (however slightly stronger than Kooiis) with the only notable drop being the Frayed Robe*.
Moving on, we get to the boars, the best money source in the forest here.
Leaf Boar':' this boar, like all boars, is an aggressive monster which you might want to take it easy with in the beginning. They are fast and pretty strong, so a horde of them might cause trouble. But once you've got control of them, you'll see they drop a pair of weapons on a surprisingly regular basis: Wooden Shortbow* and Practice Sword*. These can be sold for 250 gold each at the Secretphantom/Crimsonsabre Merchant.
Leaf Boars bigger sibling, the Angry Leaf Boar, drops the same pieces of equipment, which means that when you're hunting in the southern parts of the map where both of them hord, you will get a rain of bows and swords. That is not the best part of the boars though, for that is the Ruined Leathers they drop. Despite the derogatory name, by trading five of them to the Leather Craftsmen in town, you will get either one Cured Leather or Small Bag. If you manage to get five of the Cured Leathers, you can again give them to the Leather Craftsman and get either two Heavy Leathers , a pair of Old Leather Gloves or a pair of Old Leather Shoes. Again, if you rack up five Heavy Leathers, you can give them to the same man and he will give you a Leather Belt or Leather Gloves. If you give him ten, he'll hand you Leather Shoes or a Leather Armor.
The Heavy Leathers can also be acquired by fighting the mini-boss in here: the Bulldozer Jr.
When you have found some items, we move on:

Step 2: Selling your items for profitEdit

This step is where those who payed for Platinum in the game will have an easier time, because they have access to the Black Trader, the offline trading system. It lets you put an item up for sale and then you don't have to care anymore. Be warned, though, for the NPC take both a deposit and a commission fee for his services. The deposit is equal to the price you ask divided by 66, rounded down with the starting value at 15. (INT((Price>999)*(Price/66-15)+15)) The commission fee is the price you ask divided by 20, rounded down with the lowest possibly value being 50. (INT((Price>999)*(Price/20-50)+50))
The benefit of using the Black Trader, except the avantage of not having to shout out your sales actively in the Trade Chat, is that you despite the fees often (if not to say always) can sell for a higher price. If you were to sell the swords and bows from the boars in the NPC shops, you would get 100 Gold each (250 gold at the Secretphantom Merchant (siras) or Crimsonsabre Merchant (Lanos)).
If you aren't able or don't want to become a Premium Member, you can still sell stuff. The items I have marked with asterisk (*) will be hard to sell by word of mouth to players, so I recommend selling those to the NPC stores. The others, while sometimes cumbersome to sell, can be sold to players with a bit of effort. Check the Black Trader for current prices (even if you can't sell there, you can browse and buy).

Tips: the items I have marked with an asterisk can also be dissembled using Magic Extraction Scroll (D Class), which can be bought from Kana for 110 Gold each. If you do this, you will either get a Green Powder or a Green Crystal (although the latter is rare). While the Green Powder's worth doesn't justify the price for the scroll plus what you could've gotten from the equipment at the Black Trader, the Green Crystal can be sold for several thousand gold pieces if you're lucky enough to find it.

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