If you wish to sell CSGO skins you can do it at Steam Community Market, third-party marketplace of your choice, and at Skinwallet. Steam Community Market's biggest advantage is that it is practically impossible to get scammed. The prices are also quite high.
DMarket: Best Overall CSGO Trading Site\n\n For those interested in buying or selling items for money, the platform has a fee range of up to 7% depending on the item. Compared to most CSGO skin trading sites, it can be considered a reasonable fee. However, DMarket compensates fees with massive discounts of up to 35%.