Ok, so I havent found this on the forums, but if it is already on, just ignore me. I'm trying to contribute, but can't really be asked to look through hundreds of topics (meaning that search didn't carry any results).
So here is the actual gold-making method:
Magic happening here
There is a widely ignored recepie, called Void Shatter. It is ignored, because you can only obtain it with Honored Shattered Sun Offensive reputation.
Noone really cares about this, and it's got forgotten pretty much.
The recepie is quite easy. If the void crystals are less then twice the price of the large prismatic shard, pick up this recepie, and shatter them.
You should have a market for it, because there isn't much large prismatic shard on the market, but people usually need it.
How can you make even more money out of this ?
You can even try a monopoly with this, and I'll tell you why:
Monopolys are (in the majority of the time) a bad idea, because people try to monopolize (is that spelled right? ) things that people have a major need for.
In the case of Large Prismatic Shard people don't buy it that often (at least less often then dream shards) therefore suppliers don't supply that much, and you can easily buy up their shards (without much of a loss) and resell.
Large Prismatic Shard is also a good idea because, let's be honest, there are not many farming strategies that suggest getting these items.
If you monopolize the market, try not to dictate some kind of a huge price for it, it will never sell, I advise you to keep the price so Large prismatic shard's price equals Void Crystal's price. This way you have a 100% profit on void shatter.
Ps.: This is in fact a server dependant method, but playing on 2 servers, and looking at wowhead data I have found this profitable.
Thanks for reading, and whoever says this is common sense, well, think about it one more time.