Although you usually don't want to buy items to sell from vendor, some items can be sold for much more than you pay for them from the vendor. There are a few reasons people will buy a vendor item for a higher cost at the AH. They vendor may be hard to get to, the recipe only sells in limited stock, or the buyer simply may not know where the item is from.

Step-by-step class guides are on the way!  The 1-12 Mulgore Guide is the first guide to get all the individual class steps.  At the top of the guide, simply select which class you are playing and the page will dynamically update all the steps in the guide for that class (both text and images).  The rest of the guides will be slowly updated overtime to include all the class steps, but you can see how it's going to work with the 1-12 Mulgore.  I want to thank crazyK and his Placeholderguild for helping me out with the individual class content.  They are allowing me to get the 1-60 Alliance guide done while also getting all the class steps done at the same time, so everything can be ready for Classic launch (hopefully).

Nearly all quests offer cash or items as a reward, and often both. While completing quests shouldn't be your main form of wealth generation, it is something you are going to do anyway. The key to making the most of quests is picking your reward items wisely. Don't always pick the item that most fits your class - if it isn't demonstrably better than your current item, instead go for whatever reward sells for the greatest amount to the vendor. You can select the in-game interface option to display it in the tooltip. In general, if you can't use a quest reward for your character, pick either a plate-armor or melee weapon as your reward--these tend to sell to vendors for more than other items.
Stormheim is the zone you want to start it. For some reason Legion treasures are not worth any experience like they are in WoD...except in Stormheim. I haven't been able to find out any reason for this, and it's possible it may get fixed/nerfed at a later date. But for the time being you REALLY want to jump from treasure to treasure to augment your quest experience.
At the end of Legion, the titan Sargeras was imprisoned, but not before he plunged his sword into the planet Azeroth. This not only devastated a massive area (much of the desert zone of Silithus is now cracked and scorched), but badly wounded the gestating titan inside. While the heroes managed to ablate the worst of the damage (at the cost of the majority of their artifact weapons' mythic power), the world is still wounded and bleeding a substance called "Azerite," which has great magical potential. The Horde Warchief, Sylvanas Windrunner, attempts to consolidate Horde power on Kalimdor and gain a monopoly on Azerite (which is primarily found at the southern end of the continent). Her campaign to do so, the War of Thorns, formed a pre-launch event for the expansion and ends with the major Night Elf holdings on the continent seized or (in the case of their capital city of Darnassus) annihilated. The Alliance makes a retaliatory strike against her home base, the Undercity, which was formerly the human capital of Lordaeron. This succeeds in driving the Horde out, but before leaving Sylvanas saturates the area with disease and toxins that render it uninhabitable. With this tit-for-tat military exchange, the Horde has almost complete control over Kalimdor, while the Alliance has near-total dominion over the Eastern Kingdoms.[4] With further conflict inevitable, Battle for Azeroth takes the two factions to the continents of Kul Tiras and Zandalar to recruit new allies in order to turn the tides of war.[4]
Always check each of the prices of the item, and look over a spread of several days. This is not so important on small items, but anything that you are spending hundreds of gold on you need to check prices carefully. It is also a good idea to check a website such as Allakhazam, Goblin Workshop, Wowhead or WoWuction to see what an item normally sells for.
Many players who already have higher level characters create alts that they level to a certain point and then stop. Often, these twinks are level 18-19, 28-29, 38-39, etc. for the purpose of going to battlegrounds at the top of their tiers and kicking butt. Since these twinked characters are owned by higher level players with lots of cash, they usually outfit them with the best gear available at their level. Thus, items that require level 17-19, level 27-29, or any other items around this level, with good stats or dps, often sell for much higher prices than they normally would. This is especially true on an older server, and also especially true of blue (rare) items. In general, "good stats" include Cloth "of the Eagle" (for mages, warlocks), Leather "of the Monkey" (for hunters and rogues), and Mail "of the Bear" (for warriors/paladins)as well as weapons with these suffixes that can be used by the right class.
With the excitement of becoming Level 120 come a lot of new activities to do. However, it is particularly important to note that you should continue to complete the story mode quests. You will undoubtedly achieve Level 120 before completing your third zone, so be sure to head back and finish the story quests as they are important to unlocking game content as well as pushing your reputation levels even higher. Each zone comes with a lot of side quests that can be ignored at first as you push your item level up, complete emissaries, and do dungeons, but when you have some time, be sure to wrap up all of the quest lines in each zone to maximize your reputation potential. Reputation is the gateway to all things in Battle for Azeroth, so quest away! Be sure to use our Quest Completion Checker tool here at Icy Veins to see if there are any missed quests in any of the zones for you to go back and complete!
Of course this is pure speculation, but who thought the token would be beneath 200.000 Gold again? But the only thing important for you is to calculate at what point you make profit by selling the tokens again. If you consider it, you should take the risk! Worst case scenario: You have a lot of balance to spend for Gametime, mounts, pets and boosts/services!
Once your character makes it to Outland and beyond, cashflow frees up considerably. The quest rewards are much better than in Azeroth. In fact, a typical character will earn from 1000-1200 in quest rewards and vendor trash while leveling 60-70 in Outland, and perhaps 1400-1600 from 70-80 in Northrend. The tendency is, therefore, to spend more freely after one hits 60. However, it is important for players not to go crazy on their spending once they make it to Hellfire. One thing is, training costs, repair costs, and consumable costs are also higher. More important, there is a large purchase that you are going to want to make at some point after level 60, your first flying mount and skill. The "bird" costs 40, the skill will cost you far more. Not only that, but if you want to fly it in Northrend at level 70, you'll have to shell out another 400 for Cold Weather Flying. And for those characters who will be 'farming' herbs or ore in either Outland or Northrend, an elite flying mount is almost essential, as it helps you gather almost twice as fast. That's another 5000 you'll be looking at. Therefore, budgeting carefully during the 60-80 leveling process is essential to ensuring you have sufficient cash on hand for making those purchases. Saving your pennies early makes that bird appear that much sooner.
Congratulations on reaching Level 120! There are a myriad of new things to do. The first thing you should do is head to your faction hub ship where you have been doing your mission table quests and footholds to pick up and complete the quests necessary to unlock World Quests. World Quests will provide you an opportunity to grind reputation levels, acquire gear, and gather Azerite. There are tons of new things to do that we will cover in our Level 120 Battle Guide found here: Level 120 Battle Guide.
First of all, the value of transmog is decided by rarity and how they look. Some items like Minenarbeithut der Tiefen or Pendel der Verdammnis (they can drop in Uldaman) are worth millions of gold. They are worth so much, because they have a really small chance to drop. Other items are bought well because they look good. Best example in this case is the Glorious set, its legplates Glorreichen Beinplatte reach a 100.000 Gold value easily.