I thought I'd start a little open debate about some of the more controversial ways to make money in the game. Lots of people have opinions on different topics, and I thought I'd post a few of my own. Feel free to chime in with your own ideas, but keep it civil, please ^_^
Day-Trading
The first topic that comes to mind is day-trading. Day-Trading is, at its core, buying low and selling high on the Auction House. There are a couple of techniques to this; I call them...
A) Buy low, resell higher. The basic day-trading technique. You find underpriced items posted by players who want a quick (and guaranteed) buck instead of waiting for higher payoffs and the potential loss and resale. You buy the below-average priced item and resell it for the average.
B)Cornering the market, which has two caveats I can think of:
1) Buying out the stock. You buy out all the items on the market and resell them all for higher. If they sell, you'll make a very hefty sum of cash, but send consumers away grumbling.
2) Rare recipe monopolies: If you're one of the only people who can make, say, Gloves of Spellmastery or the Lionheart Helm, you effectively have your own market. You are free to make these items and price them without consulting the market (if they sell, well, that's a different matter). You can also charge a crafting fee and make the rare item for the materials plus this fee.
Pro-day-trading: Hands down the easiest way to make money (note: if you are good at it!). These techniques will take away hours of senseless grinding at level 60 for your epic mount, not to mention that the more money you make, the more items you can buy, opening up potential cornerings of the market.
Anti-day-trading: You are using others to make money. By cornering the market and buying out the stock, you are gouging people and charging them inflated prices that you control. In the US there are actually laws against this kind of behavior. Rare recipe monopolies are less harmful, but if you charge 100 gold for an item plus its materials just to make it, it's an extra pain for the buyer.
My take: I really like the buying low and reselling higher technique. There is nothing wrong with this, as it stabilizes prices. Cornering the market, however, is a pain in the neck. However, if a consumer does not know the normal prices and buys at inflated ones instead, then it is their own fault. The market moves in cycles; and if someone loses their deposits and needs to resell 75% of the items they bought, odds are the monopoly prices will quickly fall back to the status quo. As for the rare recipes, hey, there's nothing you can do about that buy bite the bullet and buy. You don't NEED that item, so it is up to you to cover whatever the costs are.
In groups: BoE (Rare and up) drops
Sometimes in groups some good loot will drop; a blue world drop. Hopefully loot rules have been established before so this can be taken care of peacefully. The main problems for these seem to be:
A) Need before greed ambiguities: I have always played this way with blue BoE drops: if you roll need and win, you MUST equip the item right there and then. You don't need to keep it on, but you must soulbind it to yourself. NEED means your character will use it. Not your alt, not your guildmate, but you yourself. "I need money" is not a NEED roll.
B) "I was afk and missed the roll; let's reroll": No. It was your own fault for being afk. If you missed a roll on a BoE piece, it is up to the item's winner to decide if a reroll should be held. I am of the mind that a reroll/trade should be considered only if the afked person needs (will use) the item. Greed rerolls are selfish of the afker; hopefully you won't be away next time an item drops!
C) Multiple blue wins: I see this as applying to boss drops, not random blue drops (unless you roll NEED on the randoms). If you are greeding and everyone can roll on the drops, then the one-drop rule is only in effect if the looting rules agree on it before.
Buying from (potential) gold-farmers
Gold-farmers frequently grind instances/enemies to get rare drops, and then sell them in broken English on the trade channel for ridiculous prices. Sometimes, unfortunately, only gold-sellers find the rare high-demand items. Even if buying from them supports their campaign of evil, it is usually one of the only ways to get these items.
Pro-buying: You can't find these items anywhere else. At the very least, gold-sellers provide rare items to the market.
Anti-buying: Evil! Gold sellers destroy economies. You should wait for someone else to get the items you want and buy it from them instead. So what if it takes 6 months; it's moral that way!
My take: It is situational. Recipes and patterns are decent to buy from them, since you can use them to benefit others. Rare items, however, benefit only yourself; I see buying items as doing more damage overall than good. Generally I just avoid gold-farmers like the plague.
Yup, those are all I can think of right now :) If you have any other, or any ideas, feel free to add to it ^_^