Which principle has Greg violated by ordering an expensive new trombone?

The principle that has been violated in this scenario is the principle of indemnity. This principle is fundamental in insurance and pertains to the concept that insurance policies are designed to restore the insured to their pre-loss financial condition without allowing for profit from a loss.

In this context, if Greg ordered an expensive new trombone and has not shown that the cost reflects the value lost or that it is necessary to replace what was damaged, he may be exceeding the amount needed for full compensation. The principle of indemnity ensures that an individual does not profit from an insurance claim, and by ordering an excessively expensive item, Greg risks violating that principle by incurring costs greater than what would be justified as necessary for restoration.

Utilizing this principle helps to maintain fairness in insurance transactions and prevents moral hazard, where an insured party might take advantage of their coverage.