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Selling weapons in Guild Wars 2 is a little more complicated than the commodity side of things. You can view comparable items and base your price on those as well as the identical weapons to what you want to sell. There's also item quality to consider, something which cloth, ore, and leather doesn't need to be factored in when you're selling them. The following 8 step guide is based on what I was able to deduct from the limited amount of time we've had in game. Hopefully it is timeless, but if corrections are needed then I will go back and rework this post.
Step 0: Use the Mystic Forge to turn blue and green weapons/armor into much more valuable items. Optional but a great way to make far more money from your items. For example, I had four two-handed weapons that were green and worth around 50 copper each. After combining with the mystic forge, these weapons became a single, yellow two-handed weapon worth 18 silver instantly to a buyer.
Step 1: Know What Sells.
Blue and Green weapons sell very well to leveling characters. I try to make 50 copper to 2 silver per weapon. In rare cases, I'll be able to get 5+ silver. Keep in mind that you're competing with the ENTIRE WORLD of Guild Wars 2 players, so there's almost always many duplicates of your item that you're competing against. Be realistic and go for selling lots of small auctions instead of a handful of super big payoffs. Stats that players want to pay big bucks for on weapons are +power, +condition damage, and +precision. Having a sigil already in the weapon already for crit or damage are big bonuses as well.
Step 2: Know What Doesn't Sell.
Healing Power is the least sought after stat besides +% damage to monster types. I would vendor, salvage, or offer up those weapons to the mystic forge. White items are another thing you simply don't want to sell. In most cases I actually sell to the vendor instead of salvaging white items.
Step 3: Click on the Trading Post tab.
Step 4: Click the drop down for Show Filters.
Step 5: Fill Out the Corresponding Filter Criteria
This filter criteria should be equal to the level of your weapon, category, subcategory, and only show available.
Step 6: Analyze the Competition.
Mouse over each item individually to check for the stats each possesses. Ignore items with +healing or +% damage to monster types. Pay attention to the ones with good damage stats compared to your weapon. Almost always you will see your weapon listed anyway. Compare the price of similar items as well as the # available.
Step 7: Click the Sell Tab.
Step 8: Sell the Weapon.
Sell your item for 80% of the competition's pricing so that it will sell quickly. You want the item gone and the cash in your pocket asap. If the item already is being listed on the ah and there are more than a few dozen available, open up the item and see what the "Highest Buyer" price is listed as. In most cases there will never be a buyer looking for the weapon while leveling. But it's always worth checking anyway!
I've stuck with the 80% rule thus far and things are working nicely. Sold around 20 weapons this morning alone for anywhere from 50 copper to 3 silver each.