Happy new year Ardy.
There are several sites much like that one, I have not checked recently but they used to charge fees well in excess of 30%. As a seller you would be responsible for the cost of delivery and would not receive payment for any goods sold until long after they had been received by your customer. I would seriously study the terms and conditions, especially when it comes to returns. Given that most prices have a zero added (many a 30 quid piece of glass is advertised for 300) it seems appealing but I wonder how much actually does sell. As far as I can tell customers would need to be either incredibly gullible or incredibly wealthy, then again perhaps both. My impression of the sites is one of repulsive levels of greed, on the other hand they probably provide a lot of reassurance to a nervous customer not confident of buying.
John