Laura, EZ Auto Rental (Caribou, Maine)

Around here, the worst messes to clean up are tree sap and road tar. Inside the car, my biggest issue is getting rid of the cigarette smell. A lot of people around here treat the rental vehicle like a garbage can.

To clean up smells, we use carpet shampoo, deodorizers and sometimes even engine degreasers. Scented baking soda is good for carpet stains. We use stuff you would buy for your homes.

Cleaning fee: none charged. We’re supposed to charge a cleaning fee, but we don’t. Renters complain about it, so that’s why we just don’t bother.

Lauren, Avis Rent A Car (Corpus Christie, Texas)

We use vinegar to get out fish smell. We’ve found sour milk in a vehicle which left us with maggots. We used baking soda to get that out.

We once found a rat in the engine, which stunk up pretty good. We took the vehicle to one of our body shops, and they had to take some parts off the vehicle to get the pieces of the rat out. Actually, the eyes were kind of looking at you when you opened it.

Cleaning fee: $50 and up, depending the situation.

Mike Risheill, Arena Dodge (Dayton, Ohio)

We occasionally get tree sap. We occasionally get pets that have thrown up in the back seat. We have special cleaners who clean it up for us. Everything is pretty much industrial strength. We have some aerosol stuff that we use to cover up the smell.

Cleaning fee: $50. No one objects because it’s in our terms of rental.

Ryan Fahey, North Star Rent A Car (Sitka, Alaska)

We’ve just got a small rental fleet here and the worst we get is stuff like coffee stains. We use a rug cleaner to get out the stains. We scrub it in and then we rinse it out with an extractor. It works pretty well.

Cleaning fee: Minimum of $50, up to the cost of a new interior. The renters don’t object. [PAGEBREAK] Cynde Morton, Affordable Car Rental (Oregon City, Ore.)

I don’t really clean too much of them myself. I send most of my cars to an “in and out” (express) wash. If they’re really bad, I’ll send them for a full detail.

Horror stories are plentiful. A lady got a car impounded and the car was full of half-eaten fast food. When we finally got the car out of the impound yard, a whole bunch of fruit flies came flying out of the door. We also found her underwear jammed into the glove box.

We’ve found rusty pipes and used condoms. When cleaning stuff out of a rental car, I advise using gloves. When you rent someone a car and you just require a cash-only deposit, rent at your own risk.

Tom Prunty, Alaska Car and Van Rentals (Anchorage, Alaska)

Fish is absolutely our deadliest pollutant. As it warms up, the ice melts the fish slime and it mixes with water. If the drain is left open, the mixture seeps slowly into either carpet or upholstery in the car.

We use an extractor and a product that has organisms to eat the bad stuff, but that’s only moderately effective. After we’ve cleaned it the best we can, if we think we can save it, I put an ozone machine in there overnight. Ozone will not remove the fish gurry out of the carpet, but if there are any lingering smells, it’s pretty good at killing that.

On the outside, probably the hardest thing is tar. We use mineral oil or WD-40. Mineral oil is cheaper, but WD-40 is magic for some reason.

Cleaning fee: at least $150. If we have to replace carpets in minivans, it can cost $1,400 to $2,000. The carpets alone can cost $1,200 to $1,400 from the factory.

By the time you take all the seats and side panels out you’ve got almost four hours worth of labor, and then the cost of parts and putting it all back. We put disclaimers all over the place on fish odors. We actually have that on the front of the contract.

Jimmy Osbirn, Hertz Rent-a-Car (Orlando, Fla.)

After deer hunting, there is often animal blood and guts in the back of vans.

Once one of our technicians went into a car and saw a tail hanging from under the dash—it was a live boa constrictor. We had animal control come and get the snake out. There really wasn’t anything to clean except for a big snake.

Cleaning fee: Varies. The person who checks in the car uses a chart. About 30 percent of the time, renters object to the cleaning fees. When they do, we ask them if they would like to go have it cleaned and bring it back to us.

Sharon Faulkner, Thrifty Car Rental (Albany, N.Y.)

To help cure a smelly car, I’ll use dryer sheets under seats, an open can of coffee overnight, and most any kind of strong scented cleaner scrubbed into the carpets.

Cleaning fee: All our vehicles are non-smoking, and the customer initials a specific line stating he or she will pay $150 if he or she smoke in the car. Most people are completely cooperative and those who aren’t pay the fee. [PAGEBREAK] Ben Bennani, AA Car Rental (Costa Mesa, Calif.)

Since I rent to teens 18 years and over, 90 percent of my rental cars come back trashed with leftover food, cigarette butts and soda bottles.

Cleaning fee: $10 for cars, $15 for minivans. The cleaning fee is on the walk-around form they sign.

Matthew Holowinski, Greenberg Rent a Car (Norridge, Ill.)

When I was an agency operator, the biggest cleaning nightmare was dog hair, though I’ve had cases of used diapers left in the car and kids’ vomit on the back seat. The worst mess outside of the car is when the customer drives through fresh black pavement.

At Greenberg, I have problems with customers smoking in the vehicles. One hint is to avoid car models with fabric on the doors close to the arm rest. Customers have a tendency to hold cigarettes in their hands and burn the upholstery on the doors. The best bet is to have tough plastic material on the doors. I also avoid beige interiors.

Cleaning fee: I charge customers the same as a detail at the local car wash ($75), but sometimes it’s hard to collect. Recently I put a note on the contract that I will charge for cleaning, but it is hard to argue with a customer when in his judgment the car is not that messy and he’s had it for a few months.

Mike Dabish, Rent a Ride USA (Detroit, Mich.)

The worst thing to clean out of a car is blood. It just doesn’t come out. If the stain doesn’t come out I’ll find new seats from a salvage yard.

I was spending hundreds of dollars a week on cleaning supplies from a major distributor until I went to a dollar store and I stumbled across the best cleaning products for cheap:

Rim and tire cleaner, 32 ounces - $1 (I used to pay $12 for a 64-oz jug)

Glass cleaner, 67 ounces - $1 (paid $4)

All-purpose cleaner for interior, 32 ounces - $1 (paid $12 for 64 ounce jug)

Cleaning fee: $25. The cleaning fee is stated in our terms and conditions, though we also put it on a sticker on the rental agreement and have the customer initial it at the time of rental. This makes them think twice about bringing the car back dirty.

Neil Rivel, Dollar Rent a Car (N.J.)

Give me a blood-soaked car from a gang fight any day compared to a cooler leaking fish water. To get the blood out, we’ve used a lot of baking powder to absorb what we could, and we’ve gone so far as replacing the carpet. Cleaning blood is easy if it’s leather. With cloth seats, just get new ones. Duct tape works to remove dog hair.

Once we opened the center console of one of our cars and an elderly gentleman had used it as a urinal! The manager freaked out; the wash guy wouldn’t go near the car. We called the customer and told him to come back and get it cleaned out.

We’ve found a 14-passenger van filled with cat food in every section. I informed the customer that I was going to charge an additional $100 for the cleaning of the van. I offered them the keys back and about two hours later they came back with a clean vehicle. But at that point they were past due! Poor chap. No, I wasn’t cold-hearted, though it was tempting.

Cleaning fee: up to $75. We stamp our rental folders to warn customers at our locations that have the biggest problems. And, yes, they do complain.