Most hire companies take a swipe from your credit card as security just in case you prang the car negligently. It doesn't go through as a charge if you return the car as you found it. This happens even if you have your own annual insurance policy that some people take out to cover uninsured items. All I would say is be wary of the hire companies that operate in car parks from vans. Typically, the DO You Spain companies as they tend to try it on regularly. People are attracted by rediculously low car hire prices, but get ripped by excessive fuel charges, insurance excess add ons and occasionally loss of deposits because of minor damage or even made up damage claims.
I use the companies that meet and greet you at the airport. Typically Costa Coches and Easy Option. There are others. This means you get escorted to your car avoiding long queues and are looked after and the vehicles are in good order, in other words properly serviced. I have had some new cars from the more well known companies that were in poorly serviced state. I have not used the Camposol company but when I have called at their office the package seems to be good. Worth noting with these type of companies, a full weeks hire works out cheaper that say 3 days.
Be careful,take photos of all panels of any vehicle you hire with your smart phone before you accept it and drive it away. JF