This is what some will call common sense, but then i hope this helps those who didn't think of this, to earn some money when Cata hits.
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You will need enchanting for this!
When Catalysm hits there will be higher demands on many items, mainly because there will be so many who make a new character because of the new race.
What do people do when they make a new alt? They buy ofcourse heirloom items.
And with heirloom items people need enchants, and LOTS of them.
So my suggesten is to stack up on the best heirloom item enchants there is, which is:
Weapons:
15 agility Scroll of Enchant Weapon - Agility - Item - World of Warcraft
25 agility 2H Scroll of Enchant 2H Weapon - Agility - Item - World of Warcraft
Crusader Scroll of Enchant Weapon - Crusader - Item - World of Warcraft
30 Spellpower Scroll of Enchant Weapon - Spellpower - Item - World of Warcraft
Chest:
4 to all stats Scroll of Enchant Chest - Greater Stats - Item - World of Warcraft
100 health Scroll of Enchant Chest - Major Health - Item - World of Warcraft
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These enchants will no doubt sell in no time when the expansion arrives, and because of the high demands the price will raise from 100% - 500% depending on server. Buy the mats now when its cheap and sell the enchants later for guaranteed high profit!
Hope you guys can use this!