In Rust every week new skins come out which you can buy in the same week. If the week is over the skins will never come back to the official store. So there is a good change if you buy something that looks cool, it will rise in price.
One week there was a really awesome garage door skin that came out and I thought it will rise so I bought it for 4.40€
To my surprise a couple of months later the skin is 35€ and I sold it for that price.