Holidaymakers heading overseas for Easter who have yet to book their car have already missed the cheapest deals – but they could still save money by avoiding being ripped off by unscrupulous vehicle hire outlets.

Figures from Travelsupermarket.com reveal that someone who booked a compact car for an eight-day rental in Malaga over Easter would have paid just £69 back in January. Now the cost for the same car is £117.

But getting the best deal on car hire is about more than the upfront price. Headline deals can often double in price once you get to the rental desk thanks to unnecessary extras, sneaky charges and costly insurance.

Rip-off 1. Being made to pay over the odds for petrol

One of the trickiest areas of car hire is fuel, especially if you opt for a “collect full, return empty” policy – something which is particularly prevalent in Spain and Portugal.

“This option, which involves you buying a full tank from the car rental company and returning it empty is probably the most expensive as you won’t be refunded for any petrol you don’t use,” warns a spokesman for Which? Travel. “It’s not easy to return a car with an empty fuel tank, so you’re bound to lose out. Also, you may well be charged more for the petrol provided than you would at a local petrol station.”

According to Which? Travel, a “full-to-full” policy, where you drive the car away full and return it full, usually works out as the cheapest – and easiest – option. Some firms, such as Avis, still mainly operate full-to-full.

That said, you must ensure you return the company completely full, because if the hire company feels there is room to add more petrol you could be hit with a refuelling charge.

Rip-off 2. The unwanted upgrade that costs an arm and a leg

Be on your guard if staff at the rental counter inform you that you are not being given the exact car you ordered.

While most car hire companies reserve the right to upgrade you to a more expensive model if they cannot supply the one you ordered, additional costs should be made clear.

“If you are advised that you have been given an upgrade on collection, ask if this is free of charge – or if a fee is required,” says Rory Sexton from Economy Car Hire, a broker.

“Check the rental contract before signing it. Issues such as this are very difficult to resolve retrospectively.”

If a car hire company does not specify upfront that it will charge extra for a compulsory upgrade it should give you a better car free of charge or a smaller car and refund the difference.

Rip-off 3. Paying for someone else’s bumps and scrapes

Keep an eye out for pre-existing damage not being indicated on the rental contract, as this could result in you being liable when you return the vehicle.

“Before driving away check the car thoroughly for existing dents, bumps and scratches, and make sure the car rental firm marks this down on the paperwork,” Sexton says. “If you are concerned take photos so you have proof the damage was already present. Don’t forget to check the interior too.”

Once you have noted down all the damage on the sheet get someone at the rental desk to sign it.

When you return your vehicle go through the same rigorous checks as you did at the start. If possible, get a member of staff to check the car over in your presence. If this is not possible, take a new set of photos.

If you are charged for damage, ask to see the breakdown of charges and also a repair invoice, as less scrupulous firms may charge significantly more for damage than the actual cost of the repair. If the amount is unnecessarily high, don’t be afraid to challenge it.

Rip-off 4. Overcharging you by asking for payment in sterling

Another trap to watch out for is not being given the option to pay in the local currency when you collect your vehicle – even though firms are legally required to give customers a choice. Paying in sterling can result in you being charged over the odds as firms may use an uncompetitive exchange rate.

Before entering your pin number, have a look at the amount – and check the currency being used.

Rip-off 5. Getting you to pay over the odds for inadequate insurance

One of the most costly traps you need to watch out for at the rental desk is staff insisting you buy “car hire excess insurance”. Also known as “super collision damage waiver” (SCDW), this protects you from having to pay the first part of any claim if your hire car is damaged or stolen. The excess is usually between £500 and £1,000, but could go up to as much as £2,500.

If you wait until you reach your destination to buy an excess waiver you could end up forking out as much as £20 per day. But despite the hard-sell, you do not have to take out this cover at the rental desk.

“This is a huge rip-off,” says Bob Atkinson from Travelsupermarket.com. “Do not cave in to scare tactics by high-pressure staff to try and make you buy things you do not need. A simple way to counter the high cost of ‘excess insurance’ is by buying a policy here in the UK before you set off. Not only will this cost you a fraction of the price, but it will also give you more comprehensive cover as well.”

Sites such as Icarhireinsurance.com, Insurance4carhire.com and Protectyourbubble.com all offer excess insurance.

With Icarhireinsurance, for example, you can buy a standalone policy for Europe costing from just £2.99 a day.Unlike many of the rental desk policies which exclude damage to the windscreen, tyres, and undercarriage, this policy covers for you for damage to the whole vehicle.

Also watch out for firms which try to charge you extra for personal accident insurance.

Rip-off 6. Flogging you expensive extras

Finally, keep an eye out for other “extras” at the rental desk – such as a child’s car seat or satnav – as these can potentially add hundreds of pounds to the cost of your car hire.

“Take your own baby and child seats with you – as well as your own satnav,” Atkinson says. “This could save you a fortune.”

Trip tips

■ Always book your car hire as far ahead as possible. Booking in advance is always cheaper than walking up to a rental desk.

■ Find the best deal from online agents and brokers such as Economycarhire.com and Travelsupermarket.com, as well as sites such as Holidayautos.co.uk and Auto-Europe.co.uk.

■ Consider choosing a slightly larger car than you might normally to accommodate all the passengers and luggage. Also note that “economy” cars can sometimes be cheaper than “mini-economy,” so search all car types to get the best price.

■ Read the terms and conditions of the car hire provider’s website carefully when booking. And insist that staff let you see the rental contract before you sign it.

■ Remember to take a driving licence for all named drivers to confirm your identity, and always take a credit card as the rental company will want this for the deposit.

■ Make sure you get an emergency contact for the rental company in case of breakdown or accident.

■ Be punctual about returning your car or you could face a late-return charge.

■ Keep hold of your paperwork once you get back to the UK and check your credit card statements regularly.