So 1st thing like always I'd like to apologize for my english - I don't speak it in every day matter, and use it only in internet, so don't flame me for my mistakes xD
Before you begin to read this guide note two things:
1st you probably would prefer to do most of this things at your alt, as it can destroy your reputation on your server.
2nd It works best at medium (eventually low) populated servers, but some of these tips may work as well at high-pop server (like one I play myself) if you play low-attended markets.
So this guide is bassicaly about getting rid of competition on the markets you play. For many of you it may seem common sense, but believe me there's a lot people who still don't know how to roll a market in WoW. Generally your point is to disencourage other players from entering your market. Most od people will usually stop trying to do something, if they realize it's gonna be problematic, they find roadblocka all the way and so on - and it's what you should do!
So enough plain talk - lets get to the tips!
1. FREE SERVICE!
Right now it's working like a charm due to removal of portals in dala, but it also works for proffesions. Imagine you're a mage standing in dala, offering portals for 15g, people buy them like a charm, but suddenly some noob announces 'PORTALS IN DALA 5g each!!'. You're all angry as hell, but what you should do is not give up, log out or go farming - announce giving portals for free! Everytime your opponent spam his message spam yours, you will lost a really small amount of gold for runes, but he will eventually log out or go somewhere else, and then you have your market back for yourself!! In the end it will generate you more gold than undercutting this guy and selling portals for 4g. This shows you how it works right now, but if you're not a mage you can use it also. If you are enchanter for example, and you are offering yours proffesion on trade, and someone undercuts you, just start offering enchants with no fee - when guy goes away, back to your normal fee. You will lost some gold, but if you keep doing it you will eventually scare most of competitors from spamming trade when you're in the city, as they will know you'll just offer it for free.
2. OVERPRICING
It's the thing i do most. I used to buy green gems from AH and JC-flip them since patch 3.1, at forst for enchanting mats, then for vendoring. I haven't announce buying gems on trade for simple reason - when people see someone mass buying some goods, they start to wonder why he needs it, they do research, and eventually comes into market themselves making you a competition. But recently some guy started mass advertising buying gems for 1.2g, so what I did was constantly overpricing his offers whenever he was in the city. To the point I've seen it profitable enough (1.8g for me) I did it from my main, when he bided on that I've just kept making alts to overprice him to the point of no profit. Remember you don't loose anything by doing that. Just ask ppl who /w you to COD you an item. You don't have to pay for that, but the point is to make your opponent furious enough to stop trying to take out your market. In my case after one week of constant counter-spamming I managed to get rid of this guy, and now once again I have most of green gem market to my own.
3. YOU SHALL NOT FARM!
Generally in these one it's better to have some advantage in farming towards the opponent - be druid (can gather when shapeshifted = doesn't have to summon mount all the time), palladin (10% mount speed boost) etc. Generally it works only if you have very small competition in zone you're farming. You steal nodes/herbs instead farming yourself to discourage competition. For example today during Mithril rush I went with my alt pally to farm in Badlands. It worked excelent, untill the news spread and someone came to farm as well. Most of people when they see someone from they own faction farming (or any faction if you play on non-PvP realm) go somewhere else in the zone, to maximize their gain. It's a mistake! Maybe you get a little ore more (still less than having all zone to yourself!) but when you'll be trying to sell it you will have more competition because of guy you let to farm freely. What I did was following this guy all the way, stealing all his nodes. He was frustrated, yelled at me etc, but eventually he Heathstoned, and one again i got all zone for myself.
4. TRADE UNDERCUTTING
This one is woth effort only if you're selling really expensive stuff. It's basically other method of point number 2. Lets imagine you're selling some rare item (BoE high end epic, rare pet or something like that) - when you sell it be in some low populated city (for example Silvermoon for horde or Exodar for ally). You should sell it as alt, as this method will surely get you unliked at your server xD You sell it for the price you like, but if someone shows up and undercut him, undercut him even more! If you accidentally find a buyer this way - tell him you're in other city and you will CoD him (remember CoD takes 1 hour so you surely have 1h before flamewar on trade. Generally you should monitor your opponent - he zones out / logs out - you come back to your main and offer item for the price you like!
5. OMG HE'S A SCAMMER!!11oneoneleven
I use this one only to sell PrePaid's, but there's nothing against for you to use it for other markets. For the best effect gather a group of friends. If someone offers something on trade chat accuse him from multiple characters (or even accounts - if you do it simoultaneously it will look more legit - that's whay you need friends) of being scammer, cheating etc. Answer all the ppl who /w you, you can even give some fake proofs, like fake screenshots etc. Trade chat is like troll empire - after a while a lot of people will believe this person to be a scammer, and you wont't have to do any work aymore. Such flame can go on even for weeks (I remember one legit PrePaid seller I flamed tried to sell PP 1 month later and random people accused him of scam xD). When guy flamed from all arround finally give up, you sell what you want for the price you like.
6. AH TROLL
It's the most common sense, but I post it anyway xD
This method won't give you bad reputation, but it demands a lot of time. Generally if you're selling some goods sell one (eventually one stack) at the time, or really small ammounts. If you see someone undercutting you, undercut him for just one copper (of course if he get to ridiculous low price - just buy his items xD). Main reason behind doing so is to disencourage guy from even trying to undercut you. If someone see no profit in a market most likely he will drop it. And after he will you will start to get real money, cause of lack of competition ^^
That's just a small list of things you can do by being a jerk on your's realm market. Of course there's infinite number of means you can use, but I hope this guide give you ideas you can modificate and use on your own! If you have any suggestions or other tips let me know and I'll add them ^^
Of course these are 'bad' means to get rid of competition. You can also try 'good' ones like discounts, feebies etc, but there's already be a lot of guides 'bout these, and what's even more important i prefer to be an as*hole that a good samaritan ;P