Tips: Don't buy a lemon, do get a good deal

Many considerations run through the head of someone buying a used car, and making certain that it's not a lemon is at the top of the list.

Flat 12 Gallery Owner Jeff Allen, the star of CNBC Prime's "The Car Chasers," has bought and sold used cars for decades—including in the fast-paced world of auto auctions—so he knows a few things about the process.

Here, Allen shares some tips that help make buying a used car less tricky. As a bonus, the former sales and general manager at new car dealerships discloses a secret about the best time to get the sweetest deal on a new vehicle.

Vehicle History Report

First things first. When buying a used car, ask for the vehicle history report, which usually details severe accidents, odometer problems, value and safely level. For a car that's no older than 1981, the vehicle identification number, a 17-digit serial number required on all autos, can also provide information.

"Now that the Internet is at our disposal and we have Carfax and AutoCheck and vehicle history reports—this really helps out consumers to know that they're not buying a lemon," Allen said. "And I'm not saying they're always going to know everything and they're always going to report everything. But it is a helpful tool to know where you're at."

Perform an Inspection

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Go beyond the VHR to perform a detailed inspection of the car to make sure it's structurally sound. Though this step sounds basic, it's sometimes overlooked or rushed, according to Allen.

"Look for damage. Look for things that look out of place ... [such as ] sheet metal that doesn't fit quite right," he said. "The other thing is to look underneath the car. Look at the frame rails. Make sure that nothing looks like it's been altered or welded or things that don't look correct." Also check for leaking fluids or puddles.

Examine the body; inspect for dents and especially rust, which can spread and weaken the car's structure.

A buyer who isn't mechanically savvy should bring someone who is to help spot any signs of trouble.

A car isn't necessarily bad if it has minor damage or has had a fender replaced—all used cars might need a little work, Allen said. But if it has been in a severe accident, it may be too damaged to make it worth buying at any price.

The Paint Matters

One specific detail to scrutinize is a used car's paint job. Open the doors and look for overspray, as it most likely indicates that the car has been repainted since leaving the factory. Check for any colors that look like they don't match, especially in areas that are difficult to paint, such as corners and around doors.

"Paintwork has become a real big issue," Allen said. "The dealerships that take in certified cars nowadays can't have more than one panel repainted, or it's kicked out of the certification program."

Programs have different standards for how many panels can be repainted, but buyer beware. While more than one repainted panel could mean simply that the car was keyed from front to back, it could also indicate a serious accident.

Consider buying a meter that helps measure the depth of the paint to determine if it came from the factory. Or use your hands.

"The old school way of [checking a car's paint] was to feel the edges," Allen said. "And you could always feel a factory edge of a paint job. It had a smooth feel to it. And if it had been repainted, you could feel where they used the tape line."

Do Your Research

Before walking onto a used car lot, research, research, research. Use the Internet and call a few dealerships to gather information.

"Know what the value of the car is. Know what it should look like," Allen said. "Have some common knowledge going into it. It'll make you a better prepared buyer."

Allen also worked at new car dealerships for more than a decade, advancing from sales manager to general manager. He didn't hesitate when asked about the optimum time to get the best deal on a new car.

"Hands down—end of the month, last hour before closing, and find a salesman that needs to hit his bonus," Allen said. "Those are my three keys, and it's true."