There are other methods for dealing with them. Salts were already covered above. Besides possibly reacting like a surface contaminant, as well as acting something like a grease, they also attract moisture through both the coating and concrete, forming water filled blisters. Note that often coatings fail from the inside out. This is certainly the case with blistering.
Someone has to take the responsibility, balancing effort and success against time and money.
A pre-step is to insure the strength and integrity of the concrete. Crumbling concrete is a poor or impossible surface to bond with. There are several repair or replace options, including 'sealing' the surface with a thin, penetrating epoxy or some other compatible product. Once that is done real surface preparation can begin. New concrete usually has a thin veneer or crust of very weak concrete and salts that absolutely must be removed prior to coating.