Ever taken your car in for a simple oil change — and driven away with a big hole in your pocket after being convinced your car needed other services too?

Unless you’re a mechanic, it can be tough to know when a lube shop is recommending a service because it’s essential or because it's profitable. Here's what you need to know about five common car maintenance services to help you steer clear of paying for one you don't need.

Related: Don’t Let a Car Mechanic Take You For a Ride

Fuel injector cleanings

If you’ve ever looked around the waiting area of an oil change shop, you may have noticed a poster illustrating the difference between the spray patterns of a clean fuel injector and a dirty one. Many lube shops urge customers to have their fuel injectors cleaned, promising the service will lengthen the lifespan of the fuel injector, save gas and improve mileage.

Related: 6 Ways to Save Money on Gas

According to Kelley Blue Book, fuel injector cleaning is rarely necessary — and certainly not in a car that has racked up fewer than 60,000 miles. In fact, most manufacturers don’t include the service as part of routine maintenance in new cars because improvements in design and gasoline quality means injectors are less likely to get clogged than they were in the 1990s.

If you’re having problems with acceleration or your car seems to be guzzling gas, ask your mechanic to take a look at your fuel system. Unlike a lube shop, he’ll take it apart and perform the diagnostics necessary to make sure that a dirty fuel injector is really to blame.

Air filter replacement

No matter when you last changed your car’s air filter, your lube shop technician may push you to change it again. If his argument is that a new air filter will improve your car’s mileage and performance, think twice before agreeing. According to fueleconomy.gov, replacing a dirty filter can slightly improve performance, but won’t impact mileage. That’s because modern cars constantly monitor how much air is coming in through the filter and adjust fuel use accordingly.

Also, checking and replacing an air filter is a car maintenance task most people can manage themselves. The air filter in your car is probably housed inside a plastic box under the hood. Your owner’s manual will tell you how often to replace it. DMV.org recommends changing an auto’s air filter once a year or after 15,000 miles.

If you consider letting the lube shop change the filter, ask to see it first. You need a new one only if there’s visible dust between the accordion-like folds or you can’t see through the paper creases when you shine a flashlight on it.

Related: What To Do If Your Brakes Fail

Throttle body cleaning

Over time, grit and grime can get past your car’s air filter and accumulate in the throttle body, the silvery metal part connected via cable to your gas pedal. The throttle body allows air into the engine. If it gets too dirty it can cause your car to idle roughly. Periodic cleaning is necessary (how often depends on the car), but at lube shops this service generally is overpriced. Kelley Blue Book says a throttle body cleaning can set a car owner back $80 or more for something that probably costs a few pennies to do.

Again, this is something you easily can do yourself. Auto parts stores sell throttle body cleaning solution for as little as three bucks. Follow the directions on the can.

Otherwise, ask your mechanic to clean your throttle body (if it needs it) next time you get a tune-up. It will take him five minutes, adding just a few dollars to your bill if your mechanic charges by the hour.

Frequent oil changes

The standard rule of thumb for oil changes used to be to do them every 3,000 miles or 3 months, whichever comes first. But in a 2010 interview with the New York Times, Philip Reed, senior consumer advice editor for Edmunds, said cars manufactured in the last 12 to 13 years don’t need such frequent oil changes. He explained that improvements in engines and oils may allow them to go 10,000 miles or more between changes. Let your owner’s manual be your guide to how often to change your oil, not the lube shop technician.

Related: How to Make Your Next Car Safer

Fluids and flushes

Over time, certain car fluids, such as those that lubricate a car’s transmission, do start to degrade, and neglecting to change them can lead to unnecessary wear and tear on parts. Most lube shops recommend fluid changes at standard intervals for all cars, and often push them in conjunction with a flush of the system to get rid of any residue the dirty fluid leaves behind.

But how often various auto fluids need to be changed depends on the car, not a one-size-fits-all schedule. For example, National Public Radio's auto website, Cartalk.com, points out that in many cars, the transmission fluid needs to be changed only every 60,000 to 100,000 miles. Some manufacturers recommend never changing it at all. 

Paul Hope, a trained chef and DIY enthusiast, has restored two houses and writes about food and homes.