In my opinion, best way of trading in TF2 and make profit is to spend your Metal/Keys/Buds on item you REALLY want. Don't go out and buy stuff you know you won't use. It builds up pure slowly but surely. Another good way to get rich in a semi-quick way to to craft weapons together and build up Metal from there. As for saving up keys, just buy some from the TF2 store/Steam Market, save up a few, and unbox 1 or 2 A MONTH, and there ya go. Now for buying quicksell backpacks, your on your own I'm afraid, because for 1:I don't even have the pure to buy backpacks to begin with, and secondly, as stated before, I only buy items that I know I like/enjoy OR with the exception of an item that would look great in my TF2 item collection. That's just my way of making profit in TF2, but everybody was their way of making profit.
I beg to differ Matthew. Just unbox a Burning Flames Killer Exclusive and go from there.