I rent cars from Santander airport on a weekly basis and the only compnay I have ever had issues with is Goldcar.
They are a return to the bad old days of car rental. They rent cars with loads of un-noted damage to try and add on charges for damage not caused by you. They add on bills of hundreds of euros for 'special cleaning' to remove small amounts of sand/dirt that can be removed by a hoover in minutes.
The staff are liars, they will confirm the car is fine when you return it and then you will receive additional charges in the following days.