The problem here is that if you take an insurance policy to cover tyres, glass etc which is not covered by the fully inclusive insurance that the hire company advertises, you actually need to buy the additional insurance from the hire company itself. Fully inclusive does not mean fully inclusive in Spain.
If you buy additional cover from a broker then you may have to make the security transaction as required by the hire company, AND if you do have a situation that involves such damage you have to pay the hire for it THEN make a seperate insurancce claim.
Buy additional cover from a hire company and they will process the claim on yur behalf. Hopefully, this is what a rep from Goldcar told me.
So my recommendation is to take the fullest insurances cover available from the hire company, not additional cover from a third party broker. Beware, you may find that you thinking you are dealing with a hire company but it is actually a broker. There are misleading web sites out there! See my other posts!