You shouldn't worry about these stuff. Unfortunately, instances of shops ripping off people is so remote that even I haven't heard of them especially in big-name shops. Think of it this way: some of the big known shops does installations and gears worth more than a million pesos. They won't rip you off a head unit ;)

And no, be at ease kay Jeff. Kilala yan ;) besides, sa kotse palang niyan alam mo big-time na eh :D As for the HU, whatever fits your budget. You can also say what you want and ask the installer for his advice.