Bitskins

I've used bitskins for a while, and I can say that its a good site for buying skins.

The way you have to add money, however, is terrible and sometimes impossible. I got banned from G2A (the site you have to use to add money with a bank account) after trying to deposit large amounts of money onto the site. There are a few other methods like whitelisting your PayPal account, which is a slow process. You have to know your prices, so you don't accidentally overpay since it's the seller (not the site) that determines the price, usually at least.

When it comes to selling skins yourself for real money, it's often worth it. Your item is almost guaranteed to get sold if you have the patience to wait. However, there have been issues with the site, and I do not recommend selling expensive skins unless you need the money fast and are willing to sell it for less than it's worth. (I lost 600$ because bitskin support does not care about their suppliers or customers as long as they make money)

All in all, I would recommend it if you're not that serious about skins and have money to waste. It's one of the best options for CS: GO skins at the moment.