If you damage a piece of equipment?

It's a civil matter. I would tell them that you aren't going to pay for anything at all. Tell them to take you to small claims court. In small claims court they have to prove their case. They have to prove you were negligent, but we really know they were the negligent ones. I think if you threaten not to pay they may take your original offer to pay for the cracked case, if not it may cost them more in time and money to deal with small claims court. Good Luck