Many times, as gold makers, we get dismayed if we can't make some major returns on our investments. I know I always try to focus on the highest return activities, well letting others fall by the wayside. Flipping things for twice what they cost is almost ingrained in our brains. While this of course is the easiest and fastest way of getting gold, there's no point missing out on other opportunities available. Diversify!
Quite like real life, the more you invest in profitable things, the more money you're going to have in the long run. Say (hypothetically) you are able to make a 10% return per day by using some profession, selling everything you post daily and using the new amount as investment capitol. By the end of the week, you would have (roughly) doubled the money you initially invested. Now there are of course better investments than this to be made in WoW, but know that every investment counts, small investments that sell constantly are just as good as long term investments that make tons of gold from 1 sale (such as transmog/leveling green market).
That being said you can't do everything all the time. Some days you don't play, some days you don't have time to play the AH, or only a limited time. Do what makes the most gold for you. This is hopefully something everyone already does out of instinct alone. Daily cooldowns to me alone across a few characters are more than enough for the average player to have a mass of gold, and be able to pay for what they want (within reason) in game. But just because uncut gems are 50g and the cut are 70g, doesn't mean that this 20g isn't worth your time. When I post a spread gems on my server, I sell at least a handful each day. At 20g profit per, even with selling costs factored in, it's not a negligible gain in gold each day.
That doesn't mean I'm going to focus in on JC first, by all means I'm not. I prefer to focus in on things like Inscription CDs as well as Alchemy and Tailoring before I get into any sort of mass processing of ore. Diversification is key though, and it's important to do the things that may not net you as much overall gold, but good and fast returns.
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