FreeMarket is not really free, coz sellers have to pay to post items there. There also fees for each transaction.
FreeMarket is "free as in speech," not "free as in beer." It is without restrictions, not without cost.
The fees are extremely low though. You're looking at 15 to 20 US cents to post an item and sell it. A buyer will pay about 2 cents. That's no matter how expensive the item is, and variable quantities will be in the next release, so if you sell several of an item, the fees to post per item will be even lower. Post 100 of an item, and you're paying 0.02 cents per item.