Image credit: Gitika Ahuja/ABC News

After their son was born 10 months ago, Brian and Lauren Gross of Burlington, N.J., decided it was time to sell their car.

The easiest way to get baby Ari into the 2006 Hyundai Tiburon coupe was through the trunk and then there was the dog, Laila.

"The way the car seat goes in, nobody else fits," Brian Gross said.

Even though the Kelley Blue Book value of the car was nearly $10,000, a dealer only offered $4,000. So the couple decided to sell it themselves.

Private-party car sales are up. More than 11 million cars are sold to people from people every year, according to Manheim Consulting, part of a used-car wholesale operation. And nearly 40 million used cars are sold each year, three times the number of new cars.

The Grosses posted an ad online but two months - and two price drops - later, the car with 86,000 miles on it remained unsold. Brian Gross said he'd received zero calls.

ABC News brought in Brian Moody, Autotrader's used-car expert, to help the Grosses make over their car so it could get sold and put some much-needed money in their pockets.

Days later, the Grosses had a new ad and it had been viewed twice as many times as the previous one. Though they've received a $7,000 offer on the car, they are now holding out for more.

Here are 11 tips that experts shared with the Grosses to help them turn a used car into extra cash:

Prep your car and rethink the keychain. Vacuum up the hair, empty the ashtray and get rid of the loose change and food wrappers. Empty the trunk, check the fluids - oil, brake and windshield - and get the car washed and even waxed. Don't forget about the tires.

"Even though it might be inconvenient to you," Moody said, "someone wants to picture their stuff there - not necessarily your stuff."

Be upfront and organized. Get the car inspected and have all maintenance records and warranties available.

Price it right. Check with a local dealer and online resource guides like KBB.com and Edmunds.com to come up with a price tag. That sweet spot is usually best between 97 percent and 102 percent of blue book.

Take photos - and more photos. The Gross' ad had just five pictures. Take dozens of pictures to prove that you have nothing to hide. Take shots from all sorts of angles - interior, exterior, the engine, trunk, dashboard - and then show it. And make sure the steering wheel is straight!

Make a video ad. Make your car come alive - a little song and dance never hurt - and tell its story. Be funny. Tell the world why you love your car.

Write the ad. Be specific. Focus on how the car gets out of snow well or has amazing windshield wipers. Avoid gimmicky phrases like "fully loaded" and "like new." Be honest about the car's flaws too. Show a dent. Mention a stain. This will make a potential buyer trust you because no used car is perfect and that's OK.

Advertise in three places. Most private sellers sell their cars online so check out autotrader.com, cars.com and free sites like Craig's List and Facebook Marketplace. Post signs everywhere - in the supermarket, the coffee shop, pass them out and if you have a regular mechanic, tell him/her it's for sale. Put a "For Sale" sign in the car and then drive it around town. And don't just post a phone number. Post the price too.

Dress for success. Wear decent clothes and shoes when you show your car to a potential buyer. Make sure the garage is clean, the lawn is mowed and flowers are blooming. Be confident.

Nicole Marksen, an automotive insider, also shared some don'ts when trying to close a deal.

Don't be too smooth. Marksen said most people are afraid of going to a dealership so private sellers should make potential buyers feel "warm" and "comfortable."

Don't ignore "her." Marksen said that 85 percent of car-buying decisions were ultimately made by a woman.

Don't negotiate before the test drive. "What you want to do is have them driving, really loving it, and then having that discussion after," she said.