In real life, I dabble in mill work and cabinetry. I've even build some furniture, but I didn't do with just my two hands, or a nail gun and saw. Oh no, I used many tools. Just as important as having the tools is knowing how to use these tools, and knowing what the right tool is for the job. If I tried to use a brad nailer to put up crown molding, it'd topple onto my head almost immediately. If I used my hands instead of a push stick when ripping boards, I could easily lose a finger to the blade of a table saw.
Just like in woodworking, making gold can be heavily dependent on tools, both to help, and protect you. Sure, you could repost every one of those 300 glyphs by hand, checking to see when they were undercut, and manually posting them, but that would take quite a long time. Trade Skill Master, once you get it set up and understand how it works, will make this quite easy. For me, I only use Auctionator, as it is all I currently need. I run scans to get prices on items, use it to check when items have been undercut, use it to auto-post at one copper cheaper then any other item, and cancel undercut auctions quickly. I also have it set up to allow me to buy out auctions with I shift-rightclick. Time saved here can be used crafting, doing my dailies, or even allowing me a quick AH run to repost my item enhancements during peak time when our raid team is taking a ten minute break. Heck, time saved is often used to play StarCraft 2. Making the most of the time you have, saving time where you can, is a key part to establishing your money making endeavors. Know your tools to save time!
Knowing your tools can save more then time, it could save you quite a bit of money. Once, when I didn't have my addons set up, and wasn't paying attention (no addon can fix that, sadly) I posted a few bars of truegold for 1/3rd their price. Of course, I didn't notice until they sold. If my addon was set up right, I would not have posted so cheap. Having scans of the AH can help you know how to price rare items, whether current iLevel BOEs, or rare old world drops, keeping you from underposting. They can also help you find deals. Blood of the mountain, a semi-rare drop off molten destroyers in Molten Core is used to craft the sulfurion hammer, combined with a drop off Ragnaros to make a legendary. They normally sell for between 1500-2k on my server, but I've seen a few for 250 gold, which I snapped up in a second, having scanned them for 8x the price a few days earlier. And the list goes on. Keep yourself from being burned, know your tools, and how to set them up, and customize them!
One more thing tools can help you do is to keep your self organized, useful especially if you have numerous toons or guild banks. Addons such as altaholic keep track of how many of a certain item you have across toons. Titanpanel, among other things, tracks my gold on each toon. My Sales tracks sales, average price per item, and tells me how much I collected when I close my mailbox (in the past 2 weeks I sold 110 ebonsteel belt buckles, for around 16,000g profit). Baudbag combines your bag and bank view into one, making it easier to organize things, and find things. Lets not forget Postal, one of my favorites. Opening all my mail for me? FTW! Know your tools, stay organized.
This post was aimmed more at newer players, or gold makers, and is fairly basic. If you have any questions about addons, except TSM, post a comment and I'll try to help. Next up: Learn2Gem.