We all assume that car hire firms are prone to sharp practice – billing for existing damage, over-charging for repairs – but a recent investigation into UK firm Green Motion has found some blatant abuses.

An investigation by the BBC’s Inside Out found that staff at Green Motion were given incentives to charge heavy fees for damage, some of which was already on the cars. At the same time, motorists reported huge charges for repairs, out of line with standard repair bills.

The company’s CEO defended himself, telling the BBC: “We are not aware of any franchise that is incentivising their staff to find damage.” However, a whistleblower said that if he charged the customer for damage, he would get commission and a bonus. In 2018, Green Motion was temporarily banned by the biggest web agent, Car Trawler, which operates rentals for Holiday Autos and Ryanair.

These tales are familiar. Car hire firms attract oodles of complaints and consumers can feel that they have little power and little choice, as they all seem to be prone to the same type of bad practice. However, there are a number of key ways to protect yourself:

Buy excess car hire insurance – car hire companies charge huge amounts to reduce excess of £800-900 to zero. It is far cheaper to pay a third party. I had insurance with Questor and had an accident in a hire car. The claim was made easily online and the £556 excess payment was in my account within a week.

Pick the right company – they aren’t all the same. For example, on one car hire adventure, I got a blown tyre. The company in question charged the full £800 excess upfront until they had decided how much to charge and never sent the repair bill. Shameful. More recently, Sixt had the decency to issue a bill after the repair had been made and send the garage invoice. Far more professional.

A recent survey by Which showed Enterprise scoring highly among users, with Interrent, the low-cost arm of the Europcar empire, showing the lowest customer score the report has ever seen. Goldcar and – you’ve guessed it, Green Motion – were also laggards.

Use your credit card – if you feel that charges have been taken unfairly, you can make a claim against the credit card provider.

Check the car upfront – yes, it’s tedious after a long journey, but it’s worth ensuring any damage is noted on the paperwork. Take photos if necessary. Ditto when you return the car – make sure it’s checked by an employee and any damage is signed off.

Ask for the repair bill – car hire firms have been known to claim for repairs that haven’t been made.

You shouldn’t have to do any of this, because car hire firms shouldn’t behave badly. However, until they get their house in order, you need to take some steps to avoid a big bill.