Coverages will vary from state to state. I work in the collision industry in Virginia, and we see alot variations from carrier to carrier as well. Here is an example... I just had a Subaru WRX in my shop. The owner had converted the car to a WRX STI. We're talking engine, trans, interior, brakes ect. He also did some body modifications, aftermarket air dam and on & on. When
HIS insurance carrier came to look at the car, they checked his policy to see if he had notified them of the changes/alterations. He had not. This left him with having to pay all of the differences in the parts and labor costs. Not a good day for the ol' check book. I checked with a contact of mine and found out that he would have been covered in full if he had this addition to his policy... only $25.00 per renewal

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One other point I'd like to make is that if his car was damaged due the fault of someone else, he would have been covered in full. In that case he is making a claim against someone elses policy - therefore he is not bound by this limitation.
Once again, this varies from state to state and by the insurance carrier !!!