But Australia and New Zealand score high in the honesty stakes, according to specialist firm Economy Car Hire. It reckons Spanish suppliers blight the lives of their customers by using no fewer than six sneaky tactics to extract extra cash – putting them in a league of their own compared with hire firms in other countries.

Spanish car hire firms are hot on dodgy administration charges. They often operate a ‘full-full’ policy, meaning that the car has a full tank of fuel when you collect it and you’re expected to return it with a full tank. When you return the car you get a refund for the fuel – but get stung for a hefty administration charge of between 25 and 40 euros.

Customers are often persuaded to use their credit card to pay for extras such as sat-nav or a child car seat at a desperately poor exchange rate, or get charged for damage which was already on the car. Others are hit with a surcharge of around 15 euros when they’re given a diesel car – even if they didn’t ask for one.

That’s not all. Customers who sign rental agreements digitally may receive a printed copy handed over in a sealed envelope, so that any nasty surprises are only spotted when it’s too late. And don’t fall for the insurance hard sell – you don’t need to take out local cover if you bought it before travelling.

Spain doesn’t have a monopoly on monkey business though – in many destinations there are one or two shenanigans to watch out for. Economy Car hire warns that in the USA you’re often given a ‘free upgrade’ – only to discover after signing the rental agreement that you’ve been charged for it. And customers are often persuaded to take more comprehensive forms of breakdown cover – even though the standard cover included in the rental rates is usually sufficient.

The UK is another country where holidaymakers often find themselves forking out for pre-existing damage that was already on the car when it was collected, while French suppliers often include a cleaning fee  as part of the deposit – giving them an easy excuse to charge you 50 euros if the car is not returned in what they regard as an acceptable condition.

Customers in Turkey may be hit by parking costs. When you collect the car using a meet and greet service, the parking ticket you’re given doesn’t have enough credit on it to get you out of the car park – forcing you to pay extra just to leave. In Italy you often have to queue for 30 minutes simply to collect your car – but that won’t stop you being clobbered with ‘out of hours’ fees when you eventually reach the front of the queue after closing time!

And in South Africa a contract fee of 40-70 ZAR (£2.20-£3.85) is levied on every rental simply for creating the contract.

Economy Car Hire managing director Rory Sexton said: “Dirty tricks are more prevalent in certain countries than others, with customers reporting fewer issues in countries such as Australia, New Zealand, Bulgaria, Croatia and Switzerland.

“If you are going somewhere where sneaky tactics are often used, make sure you scrutinise the terms of their booking in advance, and read the rental contract carefully when collecting the car. It’s always a good idea to book through a broker in the UK, which will provide the protection of UK consumer law.”