Group Sales prove there's (more) strength in numbers. Here's how they work: An item is made available in the marketplace with a starting price and starting stats (100/56 in the case of our first Group Sale item, the Onyx 50). Then, as more of the item are sold, its stats are upgraded. When the stats improve, the price increases too, but only for any new purchases of the item. Pre-upgrade purchases get the better stats for free! The level of stats everyone ends up receiving depends on the sales tier achieved by the end of the Group Sale (note the timer in the image, which is counting down to an end time of 2am PDT on 8/26 for the Onyx 50).

–Mafia Wars Blog