This blog post will attempt to describe some general tips on how to establish a strong economic base for yourself for any MMORPGs or virtual worlds that has an auction house. These are really just general tips, but these tips are based on the games that I have extensively played (WoW, Rift, Ragnarok Online 2, The Settlers Online, Diablo III), so the tips may be more suited for those games.
On second thought, the prices on Diablo III are so over-inflated and I've stopped playing after my first playthrough so I guess that doesn't really count... lol
Enjoy!
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Sell all event items
If there is any event ongoing when you first join the game, any event items that you can sell... just sell them. You won't gather enough in time to complete the event quests after all.
Sell all aesthetic items
Next, any aesthetic items that you find while adventuring, you should sell them at the highest possible price (do some research before you sell in order to maximise your profit). For any newbie, it's my advice to better have laden pockets to start your journey, than loads of stuff that you don't really need clogging up your precious bag slots.
Sell all items that are not for your class
If you get items that are not of your class, just sell them at the maximum price possible. Don't bother keeping them for 'your future other character/s' unless, of course, you already have the alt up and ready and that the item is of epic or better quality. For items that are of rare or better quality, you can try selling them in the trade channel, if there is one, for a quick sale. If you don't mind the wait or getting undercut, then the AH is for you.
Know the true value of the items that you're going to vendor
Know which item/s that dropped from mobs is extremely sell-able during your adventuring. You won't want vendoring an item when you could have gotten at least 500% more than what the vendor is offering you if you sell it to a fellow player even at a 'loss'. So, ask around or google to see if that item is of any particular value for any particular profession before vendoring.
Get the best paying crafting and/or gathering profession
Google for the best paying crafting and gathering profession and get them! If you're too lazy to google but have plenty of time on your hands for farming for materials, then you can just go ahead and pick from among the gathering professions. Crafting profession will take some time, but some professions are ridiculously profitable. Of course, google is not always accurate as it will also depend on your server population, supply and demand etc.
The harder way to find out which profession to take is through checking out the AH (to see what stuff sells fast and at a very high price, is easily obtainable and is highly in demand by various other crafting professions) coupled together with extensive googling. You'll need to know whether it is worth it to level up a crafting profession. If that profession has only an item that can consistently sell at a good price, then it's NOT a good crafting profession. However, if the supply is low and the demand is high, and you are confident that you can mass produce that stuff... then, do go ahead and rake in your profits!
Oh and of course I hope this goes without saying that you should sell any materials that you have left from leveling your profession, unless you will need them in the mass production of your commodities.
In Rift, I've noticed that collectables (like artifacts and dimension items) tend to rake in a lot of profit (but usually a little at a time, unless you get some rare items) besides the REX and some materials from dungeons. For WoW, toys, mounts, food buffs, potions and trinkets (and at times, lvl 85 blue, ready-for-dungeon/ PvP gear) usually sells well. On my server, inscription requires the least amount of farming to produce glyphs that sell like hotcakes :P So, yeah, like I've said, a good eye for the market trend is important. In Ragnarok online 2, I've previously created a niche in the market by selling rarer food-crafting materials for people who are leveling their cooking skills or wanted someone to cook some buff food for them.
Buying items on AH
Do not buy anything unless you are certain that it is dirt cheap. This may require a manual analysis of the price range of the items listed on the AH. This means hours of refreshing the AH and checking how fast certain things get undercut, how fast something is sold, which commodity is the highly priced and relatively easy to obtain (if you have the means to do so) before you even start to buy anything. But of course, you can take a risk from time to time and believe in your gut - they do sometimes pay out :)
You should also keep in mind the maximum and minimum listed price (doesn't matter what item it is) to get a general idea of how much money the average player have in that server. So, if you somehow got your hands on some super rare stuff, you'll know not to list ridiculous prices that will just set yourself up as a laughing stock.
Creating a niche economy on the AH
This will definitely take a lot of time and perhaps more than 1 character with different professions before you can carve a new niche to sell your items on the AH. An example of this that I've successfully pulled off in Ragnarok Online 2 (that I'm extremely proud of talking about) is creating a niche for mostly lower-level cooking materials (that are required for leveling). I've discovered that when I was levelling my own cooking profession and realised that despite having more than 100 and more of certain cooking materials, which I had thought should be enough for leveling, ended up not being enough and there aren't any/ very little of this are sold on the AH.
So, I had to take quite an amount of digging in order to find which mob drop the stuff that I want and at what percentage and to travel from the town back to the lower-level location to farm. I sold the stuff in 100 items per stack at ridiculous prices (even more expensive than the end-game materials), forcing desperate (and lazy-to-farm people) to buy the whole lot from me. Then, once they had enough, they will put up the leftovers of the materials on AH at, usually, a lower price. I will then buy them up again and resell them at 100 items per stack. Yes, I'm ruthless... but this is just business and it took me some time to find this niche and I'm wasn't going to let it pass me by lol. Soon though, some business-minded saw what I was doing and I was losing my niche... but then I had switched to another game so it doesn't really matter anymore lol :P
Do your math!
And, you musn't be lazy to do some math. Bring your calculator over and calculate how EACH item is priced. Some may look cheap on the surface, but when you calculate the price of each individual item in a stack, you'll realise that the same item sold by one person can be more expensive than the other (Common sense!). Some games will provide the price per unit along with the price per stack, but if there aren't any, you can try to find if there are any add-ons that will help you out that way - or tough luck, you will just need to use the old fashion calculator method.
Get add-ons - especially if you plan on expanding your business
Add-ons that are a must for big businesses and can be helpful for small ones too (if there are any add-ons for that game), especially add-ons for the auction house interface (Auctioneer for WoW, BananAH for Rift... etc) that will allow you to post items by bulk or 'remember' the last sold price for every item that you have posted on AH.
Second most important add-on is for your mail box (Postal for WoW and Easy Mail for Rift) because it won't be too long before your mailbox will overflow with excessive sold and unsold mails from the AH.
Lastly, if you have storage alts/ guild banks, you will need an add-on that will scan your alts and what they all have in their bags. It will be easier for you to find the item that you want to sell (when you see a golden opportunity to inflate the price lol, for example).
Other add-ons that simplifies bag interface and some other stuff can be pretty useful too. For those other add-ons, I'll leave it to your discretion. :)
Keep track of your stock
If you create alts of bank guilds, you will need to keep track of your items. You will need to use an add-on as aforementioned. If there aren't any add-ons for your game, then well, you will just have to keep stock the manual way. Take a piece of A4 notebook paper and list out the items on each of your alts. The best way, of course, is keeping stock (of the most important stuff) by memory.
Buying items off vendors and reselling on the AH
I don't usually recommend this because you will only be catering to those desperate or lazy people (which can be pretty rare sometimes). However, if that vendor item is limited in stock or is only available in one particularly inaccessible location, then by all means, do carry on!
More storage space
The question is not 'if' but 'when'. When you need more storage space, you have to find the least money-wasting route. For example, in Rift, is it ridiculously expensive to waste your REX on bank slots and slightly less ridiculously expensive on more bag slots. It's best to just use your REX on a new character slot and your new character will have access to his/her own bank and bag slots as well as being able to start a guild just so you can use the guild bank for even more storage space. The money wasted on bags to equip your character and bank slots pale in comparison to the storage space that all these trouble provide. In this case, the more important item to save on is your REX since, although its price fluctuates most of the time, it is still considered as a high-value commodity that people will bid on it up to the very last second.
If you somehow gotten several REX cheap off the AH, buy a new character slot instead of expanding your bag slot.
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Alright, I guess that's it - that's all that I can think of at the moment. By following these steps to your best of ability, you will be able to at least establish a strong enough money (in-game)-earning economy for yourself that you can create alts that you can lavish all your money on. :P
But of course, I cannot guarantee any of these methods if you are not very good at AH-ing. However, what I can confidently say is that these methods worked for me and I had successfully established strong income for my many characters on the more popular MMORPGs mentioned in my introduction.
If you have any questions, feel free to drop me a comment below and I'll get right back to you (to my best of ability). However, if you're just trying to beg money off me... well, sorry dude/gal, my guide should be able to help you more instead.... :P
Have fun AH-ing!