Learned valuable lessons today!

[chuchito]

Sorry to hear about your experience. I just have a couple of things in my opinion.
As many can agree, car audio doesn't last forever, especially if it was used. There's no telling how it was abused before it was installed in your son's truck. The installer should have made you and your son aware that the system had no warranty since it was used.

There are a few things that could have caused the speakers to not work. Either they were not a good match for the amp such as the ohms not matching the amps capabilities. The gains on the amp were not set correctly. Or there was something wrong with the amp to begin with. Maybe that was the reason the original owner of the system got rid of it. And it is also possible that your sone was playing it at max level for long periods of time which put a strain on the speakers which caused them to fail. Again, this could easily happen if the gains were set too high.

Regardless, car audio is probably one of the few things I would not recommend to buy used unless you know for sure that they have not been abused.