A brand new trailer could have problems. That is why the maker gives a warrenty. $260 sounds like way too much to adjust brakes, so besides sticking in the adjusting tool what are they doing? Pulling hubs and visually inspecting? Maybe grease on linings or parts missing. Are they checking wiring with meter and brake magnets with meters? How could anyone figure brakes are bad in the dealers lot during a PDI? A pull test may be enough to say brakes work but maybe only 2 of 4 are really working and certinly not at speed. I guess I would pay to have it fixed to my satisfaction and then threaten legal action . Help line in Trailer Life always has articles about things like this. Write them, maybe they can help.