The European Consumer Centre is advising Irish people to be extra vigilant if hiring cars on holidays during the coming weeks.
It says some tourists are being charged for damages which they are not responsible for.
The warning comes after one well known hire company paid staff commission payments each time they spotted damage to a car.
Martina Nee of the ECC office in Dublin says there are a number of ways to prevent being ripped off when returning a hire vehicle.
"Always take photographs when you pick it up, also when you drop off the car just to have proof," she said.
"Try to return it within working hours. If it's not in working hours park it in a designated spot, again take pictures as confirmation of that.
"When you get home go through your statements to make sure there's no unauthorised payment."