Even a down economy can provide business opportunities, as Washington-based Liquidity Services is proving in growing its work liquidating government and commercial excess assets. The 730-employee company runs Web sites that function as auction markets for wholesale, surplus and salvage items from commercial firms and federal, state and local government bodies. “It’s fair to say that we’re a counter-cyclical business,” said William P. Angrick III, Liquidity’s chief executive and chairman. “Corporations and, more recently, federal and state and local agencies are looking for efficiencies, they’re looking for cost savings. .