Its one of the reasons tf2 is so appealing to me, trading as a whole is the only reason i still play tf2. You could spend no money on the game and have many unusual hats just from trading. me i skipped the ref trading and started with 25 keys and have had many backpacks over 500USD. when people tell me its a scam i tell them they are lazy and dumb x10.
Pretty much what Gearhop said. There are some good unusuals that you can ONLY get through unboxing though. For example, I really want an Infernal Smoke Didgeridrongo, but there's only one in existence and it's not for sale; a lot of really nice unusuals are like this, and unless you have literal God luck, you'll just have to accept that you'll never get them. If you still want to fuck around and unbox a bunch of crates in an attempt, though, then it's entirely your choice.