Buying a car can be stressful, especially when you’re negotiating with dealers armed with tricks designed to get you to spend more money.

But when it comes to negotiating the price of a new car, there are certain things you can do to help set yourself up for success. On a recent episode of the “Tosh Show” podcast, comedian Daniel Tosh interviewed Marty Wiener, a retired car broker who spent 46 years in the industry buying cars for the rich and famous.

Wiener said that of all the negotiating mistakes that buyers make, one looms above the rest.

“You never want to say what you’re willing to pay per month,” Wiener said. “The biggest mistake people make is if they go in and say ‘I can afford $600 a month.’”

Rather than laying out how much money you’re open to spending on your car payment, you should instead determine what the dealership is willing to sell you the car for.

“That’s the first thing,” he said. “Once you’ve established that, then you want to base your payments on that number.”

Source: This is the No. 1 mistake people make shopping at a car dealership