I posted this in another thread the other week but think its equally useful here:
You have to be VERY VERY VERY careful with car hire in Europe. There are a myriad of firms primed to take advantage of the fact you don't speak the language and rip you off with false damage claims, ridiculous fuel policies and extra insurance you are forced in an awkward conversation to take out.
As a result, the best way to avoid being conned is to:
a) Avoid local firms or firms which do not have a presence in the UK. There are some large car hire groups which operate only in France, Spain, Italy etc. Stick with a major rental firm. For example
Hertz
Sixt
Avis/Budget
Thrifty/Dollar
National/Alamo/Europcar
b) You can purchase through a broker if you wish - it is often cheaper - but DO NOT buy car hire until you KNOW who the supplier is and make sure it's one of the firms in the above list.
c) The car will have an excess on it of at least a thousand Euro's. You will then have fun arguing in a foreign language over damage - perhaps even with the more reputable firms.
To avoid this, take out car hire excess insurance BEFORE you travel. It typically costs £2-3 a day in Europe. This will cover the ENTIRE excess and also cover the windscreen, etc etc. Basically, everything they will try and rip you off for. You can then decline absolutely EVERYTHING they try and sell you safe in the knowledge that even if you do damage the car, your excess insurance will reimburse you.
You can buy this insurance from a number of third party insurers. I use
https://www.questor-insurance.co.uk/ who charge £2.50 a day.
d) Only rent with a firm that offers a full to full fuel policy. ie, you receive it full of fuel and return it full of fuel. This way you pay for what you use and not a penny more.
DO NOT simply pick the cheapest possible rental and be done with it, the cheaper ones will end up far more expensive once you've gone through with the rental.
If you want, spend some reading the nightmare tales of woe on forums like Moneysavingexpert of countless people getting ripped off by European car hire firms.
I can't guarantee you'll have no issues at all but if you follow my advice above you have the best possible chance of a trouble free rental at the price you agreed at the start.