You buy a car – a used car – and take it home. At some point you may have noticed a chip on the windscreen. The car seller may already have had it repaired, or will offer to have someone look at it should you bring the matter to their attention.
Take this a step further. If the car you bought has (or had) a chip in the windscreen which later developed into a crack, whose responsibility should that be? Should it be covered under the warranty terms? If the seller is deeming the repair good enough to sell the car with it there, what happens if that repair subsequently fails or worsens? A seller might say that glass repairs are not guaranteed (then why sell you the car with one?). In the event that the chip developed into a crack, the dealer might suggest you claim on your insurance or to fully replace it. The question then is about the damage being preexisting and therefore technically speaking not insured under the current policy as the loss would have occurred before inception.
Would you accept the car seller’s offer to pay your excess? Showing you the money masks the issue as a) the damage isn’t really your insurer’s problem; b) your insurance will register a glass claim on your history and c) your insurer’s nominated repairer will probably want to chuck in a ‘copy’ glass and not a like-for-like replacement, ie, a genuine ‘OE’ part.
In most cases the insurer – your insurer – ends up taking one for the team because it’s an arrangement open for everyone to abuse. The underwriters however aren’t exactly rolling over for you. Their numbers allow for a percentage of glass claims which, compared to collision claims, is a minor loss. They have bigger fish to fry and by making such an allowance they’re simply letting you get on with it. There really is no onus; it’s just your conscience or moral compass guiding you.
A system which is easy to abuse just makes it easier for parties to shirk responsibility and let someone else put their hand in their own pocket. The wider implication of this means that more claims means higher premiums for everyone shopping for motor insurance.