As an example, I know that prices for Goblin Glider Kits fluctuates a lot. I used to sell mine for around 30-40 gold each about 2 months ago, but recently the market was flooded with them so the price is down to under 10g each on my server. By experience I am pretty certain that the prices will go up again, so right now I am hoarding them on one alt, both by making them myself and by buying them on the AH when they are really cheap. As soon as the price goes back over 20g I will start unloading them for a profit.
World of Warcraft offers a lot of ways to make money (gold). There is no one "right" way to make money, although there are some definite wrong ways! Some people like to play the Auction House, some people do their daily quests, some people tend to farm, etc. Many characters do a combination of all three of these along with other activities. Below is a compendium of money-making methods.
After completing your island expedition and second foothold, head back out to your third and final zone to quest in. Note that any legendaries you were using to level have become inactive and are merely stat sticks now. Feel free to replace them with quest gear as you obtain it. Before heading out, feel free to send your three champions out on new missions!
Tiragarde Sound and Stormsong Valley are both fairly similar zones, but Stormsong is a little longer, meaning that you might not even have to finish it to hit 120. Tiragarde also comes with a bit of a warning. There are plenty of side quests to do in the zone after you finish the story quests. Don’t do them. It’s not worth the time or the experience you’ll get.

A zygor guide is absolutely not a reliable investment, it's not going to be resaleable so you're never going to make your money back. As a purchase, at this point in the game if you need a leveling guide you shouldn't be playing the game. Leveling up is so fast, quests are easy to understand and chained, and the game puts a mark on your map for where to go for around 90% of quests. If you can't manage to follow in-game quests (possibly with a free add-on), what do you plan to do when you're done leveling? Raiding and PVPing don't just happen for you automatically.

Learned this today: posted a comment, came back later to see if there was any feedback, reloaded the page: the page posted a copy of my comment. That was not what I wanted. I just wanted to check if my comment was posted and if there were some responses. I did not want to post a copy of my comment from 5 hours ago. And, a humble guess, I think the majority of the users are not expecting such behavior either.
First off I wanna say that your guide truly did help. I was in my 3rd week playing the game and my friend kept loaning me money for mounts/gear things like that. I knew I had to pay him back at some point and just wanted a few pointers on how to make some gold to do that. What I got from your guide was MUCH more and I was able to pick out a few ways that helped me make enough gold to pay back my friend and even start earning some for myself. So just wanna say Thanks for all that!
While this is more a method than a farm, I still thought it belonged in this video.  This method takes advantage of the long forgotten spell, void shatter.  Generally because of the logistics behind how easily obtainable void crystals are when compared to large prismatic shards, void crystals cost SUBSTANTIALLY less.  The void shatter spell however turns 1 void crystal into 2 large prismatic shards.  Globally large prismatic shards are worth 15g a piece, while void crystals trend around 2-4g a piece.  Can you do the math on that?  You can literally triple your investment cost by creating more prismatic shards for your market.  All it requires is for you to get honored with the shattered sun offensive, a little known fact that most enchanters are too lazy to take advantage of.  Nobody is doing this, and on most servers the market it ripe to take over.  Don't believe me?  Check it out yourself!
The problem with Battle for Azeroth’s endgame is that a culling of abilities, the loss of Legion’s legendaries, and a lack of endgame talents means that hitting the max level doesn’t necessarily make your character more fun to play. Your character is a vehicle to explore new content, and it doesn’t matter how stunning the vista is if the core gameplay loop you’ll execute a few thousand times just isn’t fun.
After completing your island expedition and second foothold, head back out to your third and final zone to quest in. Note that any legendaries you were using to level have become inactive and are merely stat sticks now. Feel free to replace them with quest gear as you obtain it. Before heading out, feel free to send your three champions out on new missions!

SSC has been known for it's abundance of pet drops, which is why this farming spot exists.  It can only be done once a week by each of your characters, so make sure to hit it if you can.  Generally you'll want to kill all the bosses for a chance at their rare pets.  Everytime I go, I have the luck of getting one, in the video I actially got the Tideskipper to drop, and a video I done on the spot before that, I got the tainted waveling.  So yeah. It's a pretty awesome spot with high rewards and also some world drops.  I was able to snag a will of edward the odd as well, totalling a nasty 35,000g.  The most important part is that you kill the bosses, the pet drops do sell, and they are very easy to get.  Well worth the time invested.

Another question I am frequently asked is when should one use trade instead of the auction house. On most servers, the auction house tends to have a lot posted right after peak hours, say 1am server time. Combine this with the fact that a lot of people are just sitting in cities and not really looking to the auction house. This is where trade chat dominates the auction house. Tired players are looking for conversation to take their mind off of sleeping or boredom. If you can sell effectively, trade chat will make a greater profit then the auction house outside of peak hours. A few tips to polish those trading skills might include:
While the big NPCs of Battle for Azeroth have had plenty to do, the role of the player in the narrative is odder than ever. In the vanilla game, adventurers were faceless members of a larger army. We participated in great battles, but we were mostly there to shoot and loot. Burning Crusade and Wrath of the Lich King elevated the player, having NPCs marvel at us and thank us for our service. Later, in Legion, I became the Highlord of the Silver Hand and worked side by side with the biggest characters in Warcraft lore. I’ve run a garrison, saved the world, and I now hang out with the High King of the Alliance constantly.
Most heirlooms only work in a limited level range in their default form and must be upgraded to work at higher levels. That costs gold, and you’ll need around 30,000 gold to outfit yourself with a fully upgraded set (counting only those that give you bonus experience). You may need to spend some time on a boosted character to acquire the gold you need to outfit another character with heirlooms, but it’s well worth the effort.
The most important step in being able to buy a mount and make other large purchases should be self-evident: saving. Economize as often as you can, and don't buy anything unless you absolutely have to. You can burn through hundreds of gold even before level 20 by visiting the auction house for new equipment at every opportunity. If you do so, over the long haul you will be left with very little to show for it. Before level 20, keep your eyes on the prize: getting that mount. The mount helps you move faster. Faster movement means faster killing, faster questing, faster quest turn-ins, and faster leveling. It is the most important tool to fast leveling you can get at level 20, and infinitely more important than getting your hands on that Left-Handed Vorpal Cleaver of the Zipswitch that you could have purchased at level 23. Stay focused.
Changes were also made to levelling in earlier content with Legion's 7.3.5 patch. The level-scaling tech introduced in Legion not only be continued in the new continents of Kul Tiras and Zandalar, but was also be applied to content from prior expansions, allowing larger level brackets for lower level zones. Further, as previous expansions are now included in the base game, the level ranges for those expansions are now broadened, allowing players to spend more time leveling in preferred expansions and avoid others entirely. Some examples include a zone like Westfall having its level bracket (at 10–15 as of Legion) increased to 10–60, whilst continents such as Outland and Northrend sharing a 60–80 level bracket. The aim of this change is to encourage more player choice whilst levelling and to allow players to experience the full story of a particular zone without overlevelling the relevant quests.
You are right here. The Rematch string is part of the Info box, and as such it should be parsed correctly. (The string that contains the correct and breed/damage-specific min health requirements). This should be enough, but, I think there are also folks that aren’t using Rematch. They also should know of the type-specific min health requirements. Unfortunatly the default forms of the page don’t offer any detailed entries for the min health. They only offer one entry (for all damage types), and I always put the worst-case min health there (for pets that are weak against the expected damage type)
Swim Speed Potions (used especially at lvl 37 for Faldir's Cove in Arathi Highlands and lvl 57 in WPL).  Try to get multiple stacks of these.  I also recommend keeping a stack of these always in your bags.  You will frequently pass rivers and lakes and can use these potions to pass them faster through out the guide.  Please note that these potions do not stack with Druid's Aquatic Form and Glyph of Aquatic Form.