Are you referring to the sellers or the buyers?
You sell your stuff to get more credits so you can bid on stuff. I'll give you an example.
I bought a storage unit for $5. Nobody wanted it because of the super heavy old furniture. This was the last auction of the day and I didn't want to leave with nothing. Turns out he had some gold chains, tons of nice clothing, and a crazy porn collection. I gave away the furniture to a person via Craigslist. They came with trucks and cleared out the heavy stuff. I sold the gold to a pawn shop for $560. I sold the porn on Craigslist for $50. I placed the clothing on Ebay for 60 with out any success. I tried listing stuff in lots , tried everything.
So now I have a ton of clothing. I offered the clothing piece by piece in Listia auctions. Everything sells on Listia. I offered free shipping on my items using $60 of my jewelry chain money. Items with free shipping get the highest bids.
Now I have a ton of credits. I need a new iphone charger so I used those credits to get that. While I was looking for the charger I noticed a Iphone charging case so I got that along with play items for my daughter, clothing for my daughter, PS3 games and accessories, Wii, cameras, Coach bags, etc.
Don't think for it as a way to make a profit. Think of it as a way to sell your junk from storage for other people junk that you can actually use.
The key is to sell stuff that is light and you can get the most credits for and barely pay anything for shipping.
I sold a vintage Warner Brothers bracelet on Listia. They had a ton of them on Ebay and way better looking than the one I had from a storage unit. The bracelet sold for 30,000 credits. I was looking at a Kindle Fire tablet that went for 36,000 credits that day. So basically for a bracelet that is junk to me because it not my style and wouldn't sell for much on Ebay almost got me a Kindle Fire that I can then flip on Ebay or Craigslist. The bracelet cost less than $3 to ship and I did get a Galaxy Tablet later for those 30,000 credits that I flipped in $125
I just thought this would be an option instead of trashing a lot of storage items like pot holders and used items that you would normally trash or donate.
I won't lie. If you sign up to this link and have your first auction I would get extra credits.
listia.com/signup/2130898
I have sold over 200 items from storage units on Listia since November 2012. It does help you to save money of items that you would normally purchase also if you have items that you can't sell you can flip them into cell phones, laptops and tablets that would sell easily.