AS Fudjj stated, eBay is the best platform for volume sales. But I also use eCrater and Bonanzle.
Bonanzle has turned into a poor place for me but eCrater continues to give me slow but consistent sales. I have only 10 items listed but I get a sale every 2 to 4 weeks which nets me about 25 to 50 per month.
But eBay gives me the best bang for the buck. I get about .07 to .08 response/sales per each 10 auctions I list.
I list about 200 auctions at a time.
Bonanzle requires to much babysitting. There doesn't appear to be a streamlined order and a pay system but one of offer, approve and then pay. SO one has to be there all the time to approve an order.