Different laws in different states, here deadly force is justified to protect property. Not that many people would shoot someone over a car stereo. There is one instance where a guy used deadly force on a car burglar (blunt object) the perp survived but the police told the local news channel that it is legal to defend property.
§ 9.42. DEADLY FORCE TO PROTECT PROPERTY. A person is
justified in using deadly force against another to protect land or
tangible, movable property:
(1) if he would be justified in using force against the
other under Section 9.41; and
(2) when and to the degree he reasonably believes the
deadly force is immediately necessary:
(A) to prevent the other's imminent commission of
arson, burglary, robbery, aggravated robbery, theft during the
nighttime, or criminal mischief during the nighttime; or
(B) to prevent the other who is fleeing
immediately after committing burglary, robbery, aggravated
robbery, or theft during the nighttime from escaping with the
(3) he reasonably believes that:
(A) the land or property cannot be protected or
recovered by any other means; or
(B) the use of force other than deadly force to
protect or recover the land or property would expose the actor or
another to a substantial risk of death or serious bodily injury.
This hasn't always been the case, these changes happened in the last few years.
Regardless of paid training you receive, you should read your state laws. You can garner lots of info from local papers across your state and see how these matters are handled.