Have to scrub rental cars when people smoke in them

I rent out some of our cars occasionally.

My roommate and I own a ton of cars together. Frequently we rent them out to different people just for a day, week or a month. Usually we don’t have any issues with the people who rent. However, once in a while we have a guy or woman who completely ignores the signs in the car that prohibit smoking of any kind. I always tell people when they pick up our cars that they should not smoke cigarettes or marijuana in the cars or even anywhere near the cars because the smoke will get inside the car and settle into the upholstery. Well, a lot of the time people just don’t listen to our rules and then they end up having to spend money for a cleaning fee. I need to get the cars detailed plus cleaned up to remove the smell. Of course, they get mad whenever they have to spend my money to scrub the cars but it’s their own fault and they signed a paper for it. Marijuana smoke regularly makes the cars smell icky plus it takes forever to get the aroma of it out of the car upholstery. Last month this guy rented our pickup plus he assured us that he didn’t smoke anything at all, including weed. However, when the car was returned to us, the whole thing smelled just like a skunk weed. I was so mad when I smelled the yucky skunk smell of marijuana in our car. I called him up and told him that he was going to have to give me 100 bucks to scrub the car out even though he said that he had never smoked in the car at all.
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