We would all love to think our mechanic is the best trained, most knowledgeable auto professional around — but the truth is, no one person can be prepared to take on the demands of every make and model of vehicle in existence. We're all human and we all make mistakes. With complex new technologies being implemented with each new model year, staying ahead of the game is getting harder and harder. Fortunately, most shops are happy to right whatever wrong you discover — as long as you act quickly and speak up.

1. Forgetting the Shims

Have you had your vehicle in a shop recently for brake work and then noticed a little more squeaking than you're used to after driving off? Odds are your mechanic forgot to include two tiny pieces of metal that adhere to the back of your brake pads. While not essential to making your vehicle stop safely, these shims do cut down on the amount of noise generated by minute vibrations in the brake pad. If you think your brakes are louder than they should be, check with the shop. Most garages will take care of the problem at no extra charge and get you back on the road squeak-free in no time.

Bing: Brake Shims

2. Skipping the Filter

Everybody loves a deal, especially when it comes to routine maintenance. If you're one of the many who have been lured by impossibly economical oil changes, make sure the job includes a new oil filter. An oil filter is essential to keeping your engine's lubricant free of harmful contaminants. Unfortunately, if you believe your oil filter hasn't been changed, you'll have to take the vehicle to another shop and ask them to do the job correctly. An unchanged oil filter should constitute immediate grounds for a change of mechanic, since it could lead to premature engine failure, lower fuel economy and costly repairs down the road.

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3. The Wrong Transmission Fluid

It's amazing how many different types of transmissions there are on the road right now. Even more staggering are the differences in lubricant those gearboxes require. Automatic transmission fluid comes in a variety of weights (thicknesses), and some manual gearboxes simply require motor oil for lubrication. Even more confusing, some manual transmissions use fluid specifically designed for automatics. Needless to say, it's easy for a mechanic to get turned around when it comes to changing your vehicle's transmission fluid. If you notice your car or truck shifting harder than usual or grinding as you shift gears, immediately turn around and take it back to the shop. Insist on a full flush and fill, because using the wrong fluid will cause expensive damage in a hurry.

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4. Improperly Sized Belts

Most shops keep a wide selection of belts on hand to suit the vast majority of vehicles on the road. It's impossible for a garage to be prepared for every car that comes cruising onto the lift, and a mechanic may be tempted to use a belt that is similarly sized to the one called for by the manufacturer. Since belt types vary based not just on size but also profile, shape and type of material, this can lead to problems in a hurry. Using a belt not designed for your vehicle can lead to undue stress on your accessory pulleys — things like the alternator, air conditioner compressor and power-steering pump. It can also make lots of noise. If your belts are squeaking and they were just replaced, odds are you don't have the right belt for your car. Turn around and get the right equipment as soon as possible.

Has your mechanic ever made a mistake? If so, tell us how the problem was fixed.

5. The Wrong Hose

As a car gets older, manufacturers are less and less likely to continue manufacturing replacement parts. When that happens, the aftermarket industry usually steps in to take up the slack, though fit and quality may suffer as a result. This is especially true with radiator hoses. Most aftermarket companies make one hose that can be cut and bent to fit a variety of vehicles. Unfortunately, this results in added stress on plastic-frame radiators and leaks from improper fit. If you see a leak from your brand-new hose, take the vehicle back to the shop and demonstrate the problem. The mechanic should be able to solve the issue by readjusting the hose or ordering a replacement.

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6. The Wrong Thermostat

Your vehicle's thermostat is essential to maintaining proper engine operating temperature. Thermostats come in many different temperature settings, and it's easy for a mechanic to install the wrong part in your vehicle. A thermostat that runs too cool can cause the engine's oil to be thicker and not flow as quickly to important parts, while a thermostat that runs too hot can put undue stress on your vehicle's head gaskets and other seals. If your vehicle's temperature gauge seems to be too high or too low, ask the mechanic what temperature thermostat was installed. If it's outside the factory recommendations, ask to have it replaced immediately.

Bing: Car Thermostats

7. Too-Thin Rotors

If you've had your vehicle in for brake service recently, your mechanic may have asked if you would like your rotors turned. Turning essentially means shaving a small amount of metal from the rotor to take out any imperfections in the surface, which will improve brake pedal feel and reduce vibrations. Unfortunately, if your rotors have been turned too many times they will be too thin for safe use. The next time you come to a hard stop in traffic, the rotors are likely to warp or even crack under duress. If you have a vibration in your steering wheel every time you come to a stop, take the vehicle back to the shop and ask for new rotors instead.

Bing: Turning Rotors

8. Forgetting the Differential Fluid

It's easy to forget to replace the fluid in a vehicle's rear differential — and that's especially true for all-wheel-drive vehicles. While most differentials don't require attention as often as the engine or transmission, it's essential to stay on top of the factory-recommended service interval. Failure to do so can cause permanent damage to the differential, sticking you with a hefty repair bill. Simply ask your mechanic to make sure the fluid is taken care of when the owner's manual calls for the service.

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9. Remanufactured Equipment

Some shops may offer you the option of going with less expensive remanufactured equipment to replace parts such as starters and alternators. These are parts that were on another vehicle at one point, then removed and recycled by a third-party company. In many cases, these parts carry a lifetime or extended warranty, but may be more prone to failure than replacement equipment from the original manufacturer. If you've replaced a part on your vehicle with remanufactured equipment and the problem resurfaces, you probably have a defective unit. Not all recyclers are equal — do some research, and then take the car back to the shop to have the part replaced immediately.

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10. Wrong Tire Size

Having tires of the correct size on your vehicle is important in more than one way. Using the wrong size tires can cause your car or truck to handle and stop differently than it did from the factory, and it can also result in your speedometer being off by 10 mph or more. If you notice you're moving faster or slower than you used to, check to make sure the tires your mechanic selected for your vehicle are the correct size recommended by the factory. If they aren't, you might be stuck with them until you need new tires again.

Has your mechanic ever made a mistake? If so, tell us how the problem was fixed.

Article written by MSN Autos