If you go to any insurance website, the market value is probably the same because insurance company take value from same poll. Normally you have freedom to increase or decrease to certain percentage allowed by insurance company with term and condition.

So, I don;t think there is over or under value. If you go to car dealer, the value most likely would be less because they want to buy cheap for more profit

I think you read term and condition properly, what KenM is true.

I remember that there are two option. Something like Agreed value and Market Value. The Agreed one is slightly higher but you get full insured value. The other one you get current market value. I just use the market one