Outside of the specific markets you can utilize to make gold there are some fundamentals that will always remain relevant. For those of us using TradeSkillMaster to handle our auctioning the infamous cancel scan wars in certain markets can be annoying.
Cancel scanning is highly market dependent
How much value you get out of cancel scanning varies heavily from market to market. It depends on many factors, including the deposit cost of the item, how many items players buy, as well as how easy the recipe is to get.
In some markets you barely get any value from constantly reposting, whereas in other markets you need to cancel your auctions and relist them constantly to get any meaningful sales.
Cancel scanning takes a lot of time
With the Auction House throttle Blizzard added recently it takes a lot of time to run a cancel scan. When you cancel more than 65 auctions it slows down significantly. To be optimal you need to then focus on items with a high chance of selling after the cancel scanning, as otherwise you will quickly end up spending an incredible amount of time reposting your auctions.
Alchemy requires cancel scanning
A market like current content alchemy will have items that sell very quickly, that have relatively low deposit costs and the recipe is easy to get. This means there is a huge amount of competition and tons of cancel scanning. If you want to make money with alchemy you have to repost often, particularly on the weekly reset day, when players buy an incredible amount of consumables. The items still sell incredibly quickly which means that
Cosmetic markets are less prone
Many old world cosmetic markets are much less prone to cancel scanning. Any one item will sell rarely, and for items like transmog the deposit cost is significant. This means the expected value of reposting an item is very low, as the chance of getting the sale anyway is not particularly high. As such there is much less cancel scanning in these markets, as it is generally not worth it.
The easy way to take advantage of this is of course to focus on the markets you prefer. If you do not want to cancel scan too much then you can focus on items like transmog and battle pets, whereas if you like cancel scanning then current expansion markets are better. For some items like missives and alchemy consumables you have to repost auctions at rapidly to gold. Stick to whichever you prefer!