[One Star]

Has anyone has this problem? I'm not sure why the customer did not request the use of the trunk or put the grocery bags on the car floor. What is wrong with people? I don't want my rear seats dirtied or damaged. Wish the PAX would treat someone's else car as their own!

First of all you're assuming the customer even owns a vehicle and therefore would know how it should be treated.
Secondly, why do you assume the customer automatically knows where you want their bags/luggage?
Even if the customer came into your car to quick for you to get out of the car to help them put their things in the trunk all you have to say is:

"Sorry but if you want to keep your bags with you instead of putting them in the trunk then they need to stay on the floor so in case of an accident they don't go flying around possibly causing further injury".