I create the kit according to an online guide and put it in my bank alt's guild bank. Then, I invite your unguilded character to my guild and provide access to view the tab(s) where I have the kits stored. I then give you the URL of the guide I used to assemble the kit so you can compare the tab's contents with the guide. Once you make payment for the kit, I promote you to have full access to the tab(s) that contain your materials. I even throw in 4 netherweave bags to help you move everything out of the tab more quickly.
Everything is done in-game, so every transaction is GM-enforceable. If I fail to provide enough materials for you to get to 600, I'll provide whatever is missing FREE OF CHARGE even if it means I have to farm it up myself.
Trust me, this is the absolute EASIEST way to powerlevel your professions. Please add my BattleTag Malavice#1366 if you'd like to chat.
For reference, here is my old thread from Mal'Ganis: