Some are and some are not.

There are ticket consolidators which buy bulk tickets from carriers at vast discounts, add on a bit, and resell. Those tickets are not available on all flights, may have odd routings, and have burdensome restrictions, e.g. no changes of any kind for any reason. But, they may represent a good deal.

Others are simply fraudsters and a subset of mileage brokers. You run the risk of being sold what may look like a ticket but is not or an award ticket from some stranger's account which may be cancelled on the day of travel or worse yet, when you are in the middle of nowhere on your trip.

The cheapest ticket is not always the least expensive. But, that does not mean that a highly reputable consolidator who comes recommended by people you personally know and trust, is a bad deal. Just be certain to read every word of your contract and understand it before purchasing.