Buying used equipment can be a smart option for companies trying to preserve capital and reduce spending. Used equipment can cost as little as 50 cents on the dollar compared to new equipment, depending on its age. If it’s been well maintained, it can be a downright bargain.

Not all used construction equipment is created equal, however. Before you sign on the dotted line, make sure you’re getting a good deal. Factors to consider when buying used equipment include the quality of the vendor, the equipment maintenance history, the hours of use and signs of aging or damage.

1. Buy from a reputable dealer

Just as there are bad used car investments, there are bad used construction equipment investments. To protect yourself against buying a lemon, start by working with a reputable dealer or rental equipment company. You’re more likely to get a well-maintained unit made by a reliable manufacturer.

United Rentals keeps its equipment rental-ready. And, as a rental equipment provider with one of the youngest fleets in the industry, it sells its equipment when it still has extensive useful life left, noted a senior manager of used equipment sales at United Rentals. “We don’t run our equipment into the ground."

2. Check the maintenance history

The downside of buying used heavy equipment is the increased cost of maintaining an older machine, though often the math still comes out in favor of buying used. A used machine that has been carefully maintained will likely perform more reliably and have fewer service issues than one that hasn’t.

Ask for proof that a machine has received regularly scheduled preventive maintenance, including oil changes, air filter changes, fluid changes, and other manufacturer-recommended service. Also ask for recent repair records to understand what systems, if any, have had recent service. Major repairs to a newer machine could indicate a lack of preventive maintenance or a defect in the equipment.

3. Conduct an inspection

To make sure the equipment doesn’t have any obvious issues, conduct a basic inspection. What to look for? Signs of age or damage, such as rust, hairline cracks, or repair welds.

Check the oil filter’s date, which should be recent. Examine the air filter. “If it’s dirty, you may be looking at engine wear or engine heat,” said the used equipment manager, though a dusty environment could also be responsible. Check the engine fluids to see if they’re dirty, low, or contaminated — for instance, the engine oil has water in it, or the coolant has oil in it. You might even pull an oil sample and run it to determine if the oil contains metal components. (It shouldn’t.)

Check hydraulic hoses and look for worn hydraulic cylinders or leaks. Look for visible oil leaks. Examine the tracks or tires if the machine has them. Uneven wear, especially on track components, is a red flag.

For extra assurance as to a machine’s condition, bring a service technician or mechanic for their expert eye.

4. Weigh use hours more than age

An older machine may or may not have more service hours left on it than a newer machine. Check the hour meter and compare the annual usage to the average annual usage for that type of equipment. Keep in mind, however, that even heavy use may not mean the machine is done for, especially if it’s been well maintained. Take an excavator, for example. “A large excavator is mainly going be stationary — turning, loading, and digging. It may show a lot of hours but not a lot of wear on the undercarriage components,” said the used equipment manager.

Also consider the nature of the operating environment the machine endured, including the work it was doing and the weather conditions it was subjected to.

5. Try before you buy

Ask if you can test the equipment before purchasing. Make sure the equipment starts and stops as expected and that the engine, if there is one, runs smoothly and doesn’t produce any unusual exhaust. Put all the controls through their paces.

When purchasing a piece of used equipment from United Rentals, you may be able to demo it on a jobsite for a brief period.

In the end, the key to making a smart used equipment purchase is to know what you’re getting. Buying well-maintained equipment from a reputable company can help ensure you’re getting good value for your money.

After your purchase, servicing the equipment per the manufacturer’s recommendations will protect the value of your investment. If you’re buying used equipment and don’t have an experienced mechanic who can service it or don’t want to invest in running an in-house service operation, United Rentals offers a service plan for customer-owned equipment that includes preventive maintenance, inspections and repairs by expert technicians.

Marianne Wait is an editor and writer who creates content for Fortune 500 brands.