what were the disadvantages of monopolies during the gilded age and how was it used by Robber barons?

In hindsight, from the Gilded Age monopolists perspective they would say that they have pushed too far with manipulation of prices and thus brought negative reaction and counter measures from the general public. In particular, farmers in the Western country demanded that the government set maximum prices on railroads because monopolist had uncontrolled pricing power. Through the Granger movement they achieved passing of some of the 'Granger Laws' and set pricing limit on some services.

This concerned other industries as well. For example, the famous Robber baron Vanderbilt was competing with steamboat monopoly that controlled transportation between New York City and Albany. Using populist rhetoric and peoples line to bring down monopolies, he was trying to pave the way for his own business. Meanwhile, the monopolistic Hudson River Steamboat Association end up paying him a great amount of money so that he would stop doing it.