I can't speak for Synthweaving and Armormech as they are not my main crew skill.
My main has Biochem while my alt has Synthweaving.
Because I was long gone since 1.1, I have a belief that I won't be able to catch up with endgame crafter. This leads me to low level crafting. I invested time and resources to get 4 purple schematics per implants tier with appropriate stat allocation (mostly toward dps). Then, I sell them on GTN for 3 times the (expected) price to acquire the materials. I notice the market for lowbie isn't very competitive because it gives small profit. Most people buy my crafted implants within a day or two. I could sell blue implant but I think that purple implant is more attractive to people with alt. F2P will probably won't buy much.
The byproduct of this process is a lot of augment slot so I decided to go for Synthweaving on my alt (I pick class that give me +cri Synth and +cri Slicing) With little more effort, I can sell augment kit at lowest market. I sent 500k credits to my alt to unlock legacy crafting perks. Now, my alt gain 500k back. There are still more augment kit that I own. I don't want to flood the market with augment kit because I want to make it look like the supply is low.
To summarize, my marketing approach is to gain small but steady profit while maintaining a low risk. However, I can see the problem with endgame crafting. The endgame is constantly changing so there is a risk that you have to carry. Implant is different from moddable gear because people change implant as they level up.