I think Overstock is worth investigating and testing out. Definitely do some research to see if your products and pricing would be compelling versus Overstock's existing inventory. Overstock has never seemed that committed to helping out third party sellers so it's unlikely to be easy (what is?!). Buy.com is another venue you might consider. One thing about these venues is that you won't find as many other competing sellers so there is a chance you can find a decent niche.
What sort of products do you sell? Would the work on a "falling price" format? Have a look at http://pricetack.com. You could start them at retail and end them at wholesale with no fees or risk.