Your skepticism is healthy! There are definitely some predatory sites out there, but there are also some solid ones that have built a good reputation. One of the more reliable ones I’ve used is https://avan.market/ The thing I like about them is the transparency—the price you see in the dashboard when you select your skin is exactly what hits your balance. No "ninja fees" at the end. I’ve sold them some Random StatTrak skins that were hard to sell on regular markets, and it went smoothly. They also have a loyalty program or bonuses sometimes where you get an extra percentage on your items. It’s not going to give you 100% of the Steam market value (no one does, because they need to make a profit too), but for a fast, "no-questions-asked" sale, they are one of the top choices right now.