As an installer who does a lot of installs, I can tell you that most of us cares nothing about how the customer deals with his or her own equipment.
The equipment purchase is between the customer and the dealer who sold it to him or her.
If I were the customer, I'd check to see if everything was complete on everything that is shipped to me. I'd immediately contact the dealer, if something is missing, so the dealer can make arrangements for replacement parts.
Now, if you were the customer, and you damage or lose parts out of the box, then it is your responsibility.
The installer does not warrent the equipment. That is between you, the customer, and the dealer that you purchased it from. It is diffferent, if you opened up the cabinets of the receivers and played with the components inside.
If you lose the batteries, however, you might have to get new ones, or the installer might charge you for them. I usually keep a few in the truck and charge the customer less that they'd pay, if they went out and bought them him or herself, if I charge them at all. The same goes for cables, especially the cheesy RG59 coax, which I never use anyway.