How do you wire an amp?

I had an audio store install a system for me. And he wired the sub wires like I've never seen before. Both subs had to be hooked up are neither one worked. And the polarity was reversed. One side had red wire on red terminal and black wire on black terminal. The other side was just the opposite. And each side had two wires running to one of the terminals. Can someone please explain. I'm confused.