richard isn't wrong. When I see someone with uncraft items equipped, I have a reaction similar to "loving casuals". I don't write their name down on a list and hate them forever, I just think of them as someone who doesn't have the means or sagacity to get the slightly more valuable version of the items.
If I really needed to wear a hat at an exact moment in time and didn't have enough metal to buy a clean version, I would buy a dirty version. However, since I have means of getting metal and I would never need to wear a hat that badly, I always buy clean.
See, what you're buying is the value of the item, not the item itself. Dirty taunts are exactly the same as clean taunts, and nobody will know it unless they look at your backpack/loadout. But there's no avoiding the fact that it has a lower value than clean, there's less demand and vendors sell it for less. This is exactly similar to the way that promos work. Would I pay 22 keys to wear earbuds? Hell no. I would buy earbuds for 22 keys to add 22 keys worth of value to my backpack (and subtract it at the same time). Same with bills. Bills hat does not look good enough to warrant the price that it's at, but people buy anyway because it shows everyone that they are rich enough to afford it.
So does it really matter whether or not you use dirty items? No, not if you don't care that people will think you're cheap and/or bad at trading. By the way, this is the tf2economy, not the NYSE. stuff doesn't make sense sonetimes, get over it