In reply to Lankyman:
It's changing all the time - mainly against the customer.
Depends how much time and patience you've got to read the small print of the rival firms. Most people haven't, but you commit yourself by signing!
Probably best to read the T&Cs on line first - you won't be popular with those in the queue behind you if you try reading them at the airport desk!!
Watch out for excess clauses, and it generally pays to take out your own before you travel with someone like insurance4carhire. I've had good experience of claim settlement from this firm and recommend them.
Make a very detailed inspection of the car when you collect it and insist that all pre-existing damage inside and out is recorded and signed for by the company before you drive off. Check the condition of tires and wheels including the spare (including the pressure of this tire - I found it to be flat once when I got a puncture)
If arriving after dark take a torch to do the check.
Check that all tools for wheel changing are there and any legal requirements for Spain like high viz jackets and warning triangles are there. IIRC Spain requires a high viz jacket for each occupant kept in the car, not in the boot?
Check the hire company's policy regarding fuel. Generally full to full is best so long as you remember to fill up just before you reach the airport on your return. If you don't most hire companies charge an excessive amount to top it up.
Work on the assumption that they will be out to screw every last Euro out of you if they can. This applies to so called cheap "budget" hire prices, because they have to make it up somehow.
Post edited at 16:01