Some 25% of people who have hired a car have found damage that was not highlighted on the checkout sheet when they collected it.
If a hire car is damaged, the driver hiring the car could be forced to pay the first half of an insurance claim, up to the excess amount, which can be as much as £1,500.
While two-thirds of drivers say they check hire cars for such damage before they drive away, only 40% always check the wheels and tyres, according to iCarhireinsurance.com.
Together with the roof, windows and undercarriage, these are the vulnerable areas that are often excluded from the rental desk excess waivers.
Meanwhile, iCarhireinsurance.com also found that a third of car hire customers have returned a rental car without it being checked for damage because a rental desk employee was not available.
With 6% of car renters believing a rental company has wrongly accused them of damaging a rental car, not getting your car signed off when you hand it back could cost you dearly.
Ernesto Suarez, founder of iCarhireinsurance.com, offered anyone hiring a car this summer the following advice: "When you pick up a hire car, it's essential to check it over thoroughly and note every mark, no matter how insignificant on the checkout sheet, including any damage and scuffs to the wheels.
'Like writing a blank cheque'
"We see plenty of people getting charged for minor wheel damage or scratches on the bumper, which they know were on the car when they picked it up but unfortunately were not noted on the paperwork when they collected the vehicle."
He added: "Sadly, in the modern world of vehicle rental this is tantamount to writing a blank cheque to the rental desk."
Suarez said that holidaymakers could consider taking out standalone excess insurance, which are "usually much better value than those offered by the rental companies and in addition to the bodywork they also cover tyres, wheels, roofs and windscreens where pre-existing damage is often missed".
For more on excess cover see.