Paul Hendrix has sized up more than a thousand used vehicles in his 24 years in the used-machinery business. He is the equipment-pricing analyst for IronPlanet, an online auction house. “That’s a fancy name for an appraiser,” Hendrix says from his office in Alabama. “We sell everything from cars and trucks to cranes and combines all over world.”

IronPlanet backs everything it sells, which means Hendrix has to assess it right the first time or owe the buyer for a machine that doesn’t work. He says in his business, experience is everything.

“Buying used equipment is an experienced-based occupation,” he says. “The more you have and the broader your base, the more qualified you are to do the job.”

If you don’t know what to look for, you may end up bringing home a machine that costs you more than if you bought a new one, Hendrix says. You either need to hire someone to inspect a vehicle or train yourself in how to assess the equipment. Hendrix provides these eight tips that could save you from a lemon.