The insurance covers damage or theft of the equipment caused by a sudden and unforeseeable external event. This means that the event that caused the damage occurred relatively quickly. Consequently, damage caused by wear and tear is not covered. The unforeseeable nature of the event means that it occurred unexpectedly and would not have been foreseeable under normal conditions; consequently, the damage could not have been avoided. Intentional damage does not fall under the definition of "sudden and unforeseeable external event".
It is important to note that even with insurance, your customer is still responsible for the equipment. In case of theft, for example, you will have to file a criminal complaint with the police. If the customer is responsible, he/she is supposed to use the equipment consciously and responsibly.