Auto repair scams are distressingly common, with half the respondents of a recent survey admitting that they’d experienced attempts to sell them unnecessary repairs. Auto mechanics have many of us at a disadvantage, of course, because many people lack basic car repair and maintenance knowledge, so we have to take the mechanics’ word for it.

But you don’t have to be a mechanic yourself to avoid most of the common car repair scams out there. You just need to take a few simple steps.

Read your manual

The simplest thing you can do to avoid being scammed by a mechanic is to read the manual that came with your car. It will detail the service schedule you should be following, which will tell you when filters and fluids need to be changed. Knowing this schedule can tip you off when your mechanic insists that you need a “fluid flush” to keep your car running well—for example, many newer cars have a “lifetime” transmission fluid that shouldn’t need replacing at all, or only after 100,000 miles have been put on the car.

Some auto repair shops will lure you in with a super-cheap oil change or tune-up service that they actually lose money on, then suggest you need a full engine flush for a nice upsell. But if you know how long your fluids are meant to last, you can be ready for the trick.

Take photos

Before bringing your car to the mechanic, take some photos—inside and out, including the engine. This will document the condition of the car before the mechanic got their hands on it, which can come in handy in general if there’s new damage when you pick the vehicle up. But it also gives you a way to tell if certain parts have actually been swapped out as promised (and that nothing was switched out without your knowledge, like a brand-new battery replaced with a rusty old clunker), and allows you to compare the new parts to the old. It also serves as a reminder to check stuff like oil caps and battery straps to ensure that no steps were skipped.

Change the filters

If you have some basic mechanic skills, a terrific way to detect a scammy mechanic is to change your air and oil filters before you go to the shop—or mark them with a Sharpie somehow. This will help defend against one of the most basic scams mechanics pull: bringing out a filthy air filter and telling you you absolutely must replace yours. If you know your filters are brand new and they pull this, you know immediately you can’t trust a thing these people tell you.

Ask for the old part(s)

Finally, if your mechanic tells you that something expensive has to be replaced, a simple way to protect yourself from being scammed is to ask to have the old part (you actually have the legal right to these parts in many areas). This allows you to see the wear and tear for yourself, and prevents a scammy mechanic from billing you for a replacement part they didn’t even bother to actually replace. Even if you wouldn’t know a worn-out brake pad from a brand-new one, just asking for the old part puts the mechanic on notice that you’re paying attention.