I've sold a lot of things there over the last several years. They do charge you a portion of the final auction price, a "final value fee", but it's not too bad considering you have a huge audience looking at your wares.
My only advice is be honest about the condition, try to take several good pictures in good lighting, not blurry dark cell phone pics of your feet in socks standing next to some gun lying on the floor with dirty clothes strewn around, and service the sale promptly - contact the buyer quickly after the auction and ship the item as soon as you can after payment arrives.
First time listing is a learning curve much like anything new but it's a good website overall.
