One of these groups was operating a "work at home" scam for a while, where they were convincing people that they could cash checks, wire about 80% of the money to a recipient, and keep the rest as a fee. After two or three small checks cleared, they would hit the "worker" with a couple of larger checks in reasonably rapid succession. Due to U.S. banking laws the checks would appear to clear and the funds would become available, and the "workers" would diligently forward the money. Then a few weeks to months down the road the "worker's" bank would dishonor the checks and demand the return of its money or deduct it from the "worker's" account.
Another common version is to buy an expensive item on eBay, overpay by a couple of thousand dollars, and ask the person to refund part of the overpayment via wire transfer. If all goes well for the person committing the fraud, they get both the item they purchased and some spending money before the eBay seller finds out they paid with a fake check.

