How to pay less for a rental car

If you have a poke under the bonnet of the rental car industry, you'll find it's nowhere near as shiny as it looks in the brochures.

Many companies make their money by selling you unnecessary add-ons and charging hefty "administration fees", causing the unwary traveller's budget to disappear in a cloud of oily smoke.

We've put together 10 steps for navigating your way through the car rental process without being driven round the bend.

1 Shop around

It almost goes without saying, but the first thing to do is check out major price comparison websites like Kayak and Travelocity.

These allow you to check out hundreds of listings at once, but you should also check out the main operators' own websites.

Sometimes they run promotions or deals that aren't picked up by the aggregators, and you may be able to get further discounts.

We managed to knock more than $50 off an Avis booking by using one of the recent coupon codes collected here.

2 Smaller model

Do you really need a giant SUV to take an intrepid trip to Wellington?

Car companies will always try and upsell you from a sensible compact car to a more spacious set of wheels, because they can charge twice as much.

A week's holiday pottering around Paris will cost you about $300 in a small Citroen hired from Avis- and more than $800 in a much larger five-door model.

Resist the temptation, and you might just get lucky anyway. Rental companies only have a certain stock of available cars, and compacts are by far the most popular. If they run out of cars ahead of your booking, they might upgrade you free of charge.

3 Decline extra insurance

Almost every company has compulsory full insurance cover for their vehicles.

But they'll also try and sell you add-on insurance cover which reduces your excess, sometimes to zero.

It's a huge money-earner, playing on the fears of tourists who don't want the stress of paying for a fender-bender. They give it cutesy names like "Relax" or "Peace of Mind" cover, but it's usually very poor value for money.

Hertz' "Accident Excess Reduction", for example, adds $28-$34 to your bill every day.

Avis charges $24 per day to reduce a whopping $3450 excess to $345.

Local companies like Omega charge a somewhat more reasonable $12 per day.

You'd happily drive your own car around all year with the full knowledge that you'll pay an excess if you have to make a claim, so why would you panic over the use of a car for a couple of weeks?

Weigh it up carefully, and don't forget to check if your own credit card or travel insurance already has you covered.

4 Avoid airports

Hauling your luggage straight from the carousel into the trunk of a rental car is convenient, but it comes at a price.

Avis charges a $40 airport/ferry fee, and Hertz charges $46, so you want to avoid picking up a vehicle directly from the airport if possible. It may even work out cheaper to get a shuttle into town and pick up your car there.

5 Take photos

What happens if a bill for damage you don't remember causing shows up on your credit card statement?

Arguing with a stroppy European rental company agent when you're already back on home turf is a futile exercise.

Rental cars are often covered in minor dings and scratches, so you need to make sure you don't become a convenient scapegoat.

Use your cellphone or camera to take date-stamped photos or a video while you're in the parking lot, and get the attendants to sign off any notable dings before you leave.

6 Bring your own

Car companies make a fortune by renting out car seats for those with a baby on board, averaging an extra $13 or so each day.

It might seem like a hassle to bring one from home but most airlines are actually very family friendly. Both Air New Zealand and Jetstar, for example, will generally let you check in a car seat or booster seat for free.

Renting a Satnav device is just as wasteful. Most companies charge $10-$12 a day, meaning after a couple of weeks you could have bought a brand new GPS for the same price.

Instead you could just install a free navigation app on your smartphone, like Google Maps. Check your data plan first though.

7 Fill your own gas

Another sneaky way the rental companies make money is by moonlighting as the world's most expensive petrol stations.

Some will try and sell you a full tank of gas when you pick up the car under the guise of convenience. Unless you manage to return it perfectly drained with the fuel light flashing, you've wasted your money.

Others will send you on your way with a full tank and make no requirements for how it's returned. Then they'll charge you a fortune to top it up, usually with an "administration fee" on top.

You should always insist on leaving with a full tank and returning with a full tank. Keep an eye out for handy petrol stations when you're picking the car up.

8 Don't speed

What's worse than picking up a $50 speeding ticket while you're trying to enjoy a relaxing holiday?

Being slapped with another $50 by the rental car company to add insult to injury.

That's the outrageous fee that Hertz charges for the arduous task of a) charging your credit card, and b) processing and sending on any notices related to the offence.

Avis charges $30 plus GST, and others are in a similar range. There's nothing you can do about it except drive like a nana when you're using a rental car.

The same "administration fees" also apply to toll roads. In New Zealand you only have to worry about the Northern Gateway, but if you're heading overseas make sure you're fully paid up.

9 Clean up

Now we're starting to see why one of the biggest rental companies is called 'Hertz'. Brace your wallet for more pain - if you make a mess in the car, you'll be charged as much as $250 (plus GST) to get it cleaned.

"This includes, but is not limited to, cleaning and/or deodorising necessitated by spillage of fluids, food, vomit, stains, smoke, unpleasant odours and animal hair," Hertz says.

What if you pick up a thick layer of dust on a gravel road? Omega charges a $150 cleaning fee - or the equivalent of three days' extra hire - for vehicles that are "extensively dirty outside or inside".

At those sort of prices, it's definitely worth giving the car a decent clean before you return it. Even going through a carwash or getting a paid clean will be worthwhile for serious messes.

10 Pay promptly

Here's the finishing touch. Rental car companies will take you to the cleaners if you fail to pay any of the costs mentioned above.

Usually they already have your credit card details on hand, so they can charge you at their convenience.

But if for any reason your credit runs dry or you can't pay, beware.

Avis charges a late fee of $50 and then 10 per cent interest compounding daily.

Hertz charges 10 per cent above the interest rate it pays its bankers for an overdraft - so possibly as high as 20 or 30 per cent. Those are some seriously weighty charges.

Almost all of the above is there in the fine print, so make sure you read it carefully and don't cave in to sales pressure.

Otherwise you may find yourself being taken for a very unpleasant ride.