It depends how they rate the car. Here in switzerland, there is some "booklet" called "eurotax". There you can find any car which isn't older than 10-15 years IIRC. It will tell you how much a car is still worth after a certain time.
Insurance companies are usually going by that.
If a car is not in this booklet anymore, or is a classic or something like that, then they have to look at the average price which is payed on the market. If this is not the case in Finland (which i don't know), then there is nothing you can do about it.