Hiring a car isn't cheap, especially when you're hit with a host of extra charges when you get to the rental desk.

Here are seven rental firm rip-offs to avoid.

1. High excess charges

Although insurance will be included as part of your rental agreement, it’ll come with a hefty excess that could see you stumping up as much as £2,000 towards the cost of any claim.

The reason this excess is so high is because hire car insurance, or collision damage waiver (CDW), doesn’t work like normal car insurance.

Instead of being an arrangement whereby the insurer covers the cost of repair, it’s just an agreement from the rental firm to waive any repair costs should you be at fault for an accident.

So it’s a good idea to take out excess waiver insurance, a standalone policy that will pay these potentially pricey excess fees – just make sure you shop around and take out cover before you travel.

You can pick up excess waiver insurance for as little as £3 a day by comparing prices online, but take what’s on offer at the rental desk and you could get stung at a daily rate of £30.

Tip: Save around £17 a day on insurance by comparing prices online.

[Related story: Is it worth having a cosmetic car insurance policy for scratches and dents?]

2. Young driver fees

If you’re a young driver, you’ll be used to paying through the nose for your car insurance, and you can expect more of the same when it comes to hiring a car.

If you’re under 25, you’ll get hit with a young driver surcharge that is usually upwards of £30 a day – which comes out an eye-watering £420 extra on a two-week holiday.

And if you’re under 21 there’s a good chance you’ll be turned down for car hire altogether.

There’s no real way around this unless you’re travelling with an older driver, in which case it’s probably best to just let them do the driving.

Tip: Save £30 a day by letting an older driver take the wheel, or consider taking your own car abroad (just make sure you’re insured to drive overseas).

Car rental: how to cut costs

3. Satnav rental fees

If you’ve ever tried to negotiate narrow European roads while a co-pilot navigates using a map, you’ll appreciate how much hassle you can save with a satnav.

Of course, rental firms know these gadgets can be invaluable and so hiring one can cost as much as £10 a day.

Save money by packing your own satnav, or getting a reliable route planner app on your smartphone. There are even free apps available for download, such as NavMii, although these might not have the most up-to-date routes installed.

And you may as well pack that map too, just in case…

Tip: Save around £10 a day by packing your own satnav.

4. Car seat hire costs

If you have young children, make sure you take their car seats along for the ride as rental firms charge around £10 a day for baby or booster seat hire.

Even if the hire company only charges for a maximum of seven days, as many do, this will still see you unnecessarily out of pocket to the tune of £70, and that’s just for one child!

You could buy a new seat for half the price – perhaps even an inflatable one to save space – and take it as carry on luggage.

Tip: Save around £10 per day, per child, by taking your own baby and booster seats.

[Related story: Why cheap travel insurance isn't always worthwhile if you need to claim]

5. Additional driver fees

Having someone share the driving can make life a whole lot easier, it can also make your road trip a whole lot more expensive as additional driver fees clock in at anywhere between £5 and £10 a day.

And although most rental firms cap the charges to keep prices down for longer breaks, costs can still stack up.

To avoid this extra fee, either look for a rental firm that allows you to add a driver without charge – some offer this for the main driver’s spouse – or simply designate one driver for the whole trip.

Tip: Save as much as £10 a day by ditching the additional driver.

Car rental: how to cut costs

6. Overpriced fuel

Most rental firms offer a ‘full-to-full’ fuel policy, whereby you pick up and drop off the car with a full tank of petrol, while others prefer a ‘fuel empty’ policy, which means you pick up the car with a full tank of fuel and are expected to return it empty.

In this instance, the rental firm will charge you for the full tank, usually at an inflated price.

And if you don’t use it all up, you’ll find yourself even further out of pocket.

Tip: Save £15-£20 by opting for a rental firm offering a ‘full-to-full’ arrangement.

Compare travel insurance quotes and see if you can save

6. Extra mileage and border fees

Some rental firms will hit you with extra charges for exceeding an agreed mileage limit and travelling across borders.

So if you’re going to be racking up the miles or travelling through more than one country, work out in advance roughly how far and where you’ll be travelling to and make sure any rental agreement fits in with your plans.

[Related story: How to get over-50s travel insurance for less]

7. Charges for damage

Some of the more unscrupulous car hire firms may try to hold back some of your deposit and claim you returned the car with damage.

To protect against this, make sure you thoroughly check the car over both inside and out before signing any rental or return agreements.

It’s also worth taking pictures of the car before you take it away and as you drop it back so you can dispute any false claims, should the need arise.

And, on the subject of deposits, be aware the car hire company will require a deposit before you drive away, and this is usually done by ring-fencing an amount on a credit card, so make sure you can cover this cost with your plastic.

If you do get home to find money has been taken from your card, or you have any unresolved disputes with a car hire company firm, use British Vehicle Rental and Leasing Association’s conciliation service or the European Car Rental Conciliation Service to help settle any differences.

Compare travel insurance quotes and see if you can save