Yes it is common. Many times an asset disposition company is hired to dispose of the property. They assign the ;roperty to a brokerage. Before the brokerage gets a price from the dispostion company the property needs to be prepped for sale. Changing the locks, trash out, perhaps even cash for keys or evictions, etc… Many times the property is ready to sell before the price is given to the brokerage. In that timeframe (or even before so) there is nothing stopping the broker from marketting the home, even taking offers on it. Many times the sign goes up immediately after the broker has received the assignment from the disposition company. However the home cannot go on the MLS because there is no price yet.
Many disposition companies will ask the broker to keep the home on the MLS at least a few days. Some do not. Also yes there are brokers who cheat the system to double end the deal.