Its quite a simple way to make money in my opinion and on my server have been making a lot of money with this idea. It wont work on all servers though as your economies etc will be different but its worth a couple of looks in the AH to check...
Basically just buy cards from the AH (Beasts, Warlords, Elementals and Portals) i would stick to the one that you can make the most money from at first. Bid on the cards when they are cheap or BO when they are cheap and usually you can get the 2,3,4,5,6,7,8 for about 100g (on my server and if you arent rash with your money) this is the easy part. Next you need to get the ace (Beast's ace is hardest simply because of the drop rate or cost, about 300 for beasts) Once you have all the cards create the deck and put it into your bank and wait untill the few days before the faire arrives...its at this point which everyone starts buying up cards and decks (because its the only time you can use them) and put your decks in the AH (no more than 1 of each deck at a time) and sell for the highest price you can on a server. You should be making about 200g per deck and you get get 1 deck every week (of each 4 type) if you can afford this. This means you could (server permitting etc) be earning about 600-800g a week with practically NO effort.
In short - Have enough gold to buy all the cards in a deck...buy them...make the deck...sell in AH appropriatly...make lots of gold.
I have gone from 400g to around 1600g (i have only been doing this a month) without any additional grinding aswell as buying items and keeping a deck for myself.
Tips : Beast's deck almost on every server is the most expensive...mainly becuase of the ace being a 3% drop from a UBRS boss (the beast). If you estimate how many runs will down this bloke a day you will realise you will only see 1/2 of these in the AH a week....
Be carefull when starting to buy the decks...just write down how much the deck will cost you to make...and how much it sells for otherwise you could end up losing money.
You need to have money to start with, sadly the old saying "it takes money to make money" is true...but its a good way to avoid any more money grinding.