Alright, this works VERY well but you have to invest some money. The secret is that people will CoD these items to you for much cheaper than they can sell on the AH.
1) First you need to have some gold. 200 or so will suffice for a while.
2) Make a macro. Have it say something like "Buying Primal Fire 20g/Primal Water 18g/Netherweave 2g a stack/ Please COD at any time" etc. Just make sure they are below AH price by a good bit.
3) Use this macro every now and then. People will start mailing items to you and you can just resell them at a higher price on the AH. Most people want to just get rid of their items so they will hand em over for cheap.
Edit: Netherweave was supposed to be 2g a stack.