Not long ago, John Irvin was selling women's shoes in the Nordstrom at an Arlington, Va., shopping mall, pulling down about $20 an hour.

Now he flips houses in Northern Virginia - scooping up short sales, rehabbing them and aiming for a quick sell. He has sold three homes so far and says he netted more than $30,000 in profit each time.

"If I do one house every quarter, I'm making $125,000 a year - at 25 years old," Irwin said. "All my other friends, they have a 9-to-5 job. They make probably half of what I'm making right now. It's kind of like hitting the lottery."

Flipping earned a bad reputation during the housing boom thanks to speculators who bought and sold millions of homes in search of easy profits. But the practice is gaining popularity again as the nation's real estate market shows signs of life. The number of flips rose 25 percent during the first half of 2012 from the same period a year earlier, according to research firm RealtyTrac, and the gross profit on each property averaged $29,342.

RealtyTrac Vice President Daren Blomquist said the resurgence in flipping offers another indication that, in many parts of the country, housing prices have finally stopped falling.

 "There are flippers in any market, but a market where home prices are appreciating is much more forgiving for flippers than a market where prices are depreciating," Blomquist said. "We have turned that corner in a lot of places in the last six months, so that's going to attract flippers."

Areas of the country that were hit particularly hard by the housing crash have seen the most pronounced boom in flipping, as investors gobble up foreclosures and short sales - properties sold for less than the owners owe on the mortgage - and resell them to buyers eager to take advantage of record-low interest rates.

 The Phoenix area leads the country with nearly 10,000 flipped properties during the first half of this year. Las Vegas, Los Angeles, Miami and Atlanta also are high on the list.

 "Loan applications have tripled in the past few months," said Justin Konz, an executive at Chantilly, Va.,-based Restoration Capital, a "hard money" lender that provides fast, short-term financing to flippers. Konz said the firm funds everyone from weekend warriors flipping a house or two a year to professionals turning around dozens of houses a month.

"We thought it would slow down in the colder months," Konz said. Instead, he said, business has picked up heading into the fall, with few signs of slowing.

With numerous investors and home buyers vying for a small list of available properties in the District and close-in suburbs of Maryland and Virginia, bidding wars and outsized offers have become a routine part of the landscape. The average gross profit for flipping a home in Maryland and Virginia is about $55,000, and it's even higher in the District, according to RealtyTrac.

 "It's very competitive for people doing what I do, and the margins are very thin," said Jud Allen, co-owner of Washington, D.C.-based Express Homebuyers, a company that flips dozens of local properties a year. "The upside is, if you can find a deal, you know you can sell it and make some money. The difficulty is in finding the deals, not selling the property."

The flippers flocking to the market today are often a different breed than the opportunistic investors that helped fuel the housing boom.

"The flippers we saw going crazy at the height of the real estate bubble were very speculative in nature and were solely relying on home price appreciation to continue at a torrid pace," said Blomquist of RealtyTrac. "The flippers we're seeing these days have to be much more cautious. . . . They're not just relying on time to increase the value of the property; they are improving it."

 The new generation of flippers can still frustrate some would-be home buyers by snapping up properties with cash offers and exacerbating low inventories in certain markets. But Blomquist said they also are playing a useful role.

 "I'm sure there are still some bad players out there," he said. But "the type of property flippers we're seeing do provide an important function toward getting us to a recovery. They are taking distressed inventory others are not willing to take on."

 Doug Clark, a veteran real estate investor in Utah and co-host of the Spike TV show "Flip Men,"doesn't miss the boom days when home flipping reached stratospheric levels.

"Everything was speculation. Anything you bought was worth more the next morning. . . . You can't do that these days and stay in business," Clark said. Instead, he said, being successful requires a keen eye for undervalued properties and a willingness to put in the work required to make the houses attractive to buyers.

 Irvin, the 25-year-old flipper in Virginia, carefully researched each of his three properties - one in Dale City and a pair in Manassas - before buying. He said he spent tens of thousands of dollars improving the houses, refinishing hardwood floors, updating bathrooms, installing new kitchen cabinets and appliances, and landscaping yards but stuck to a tight budget to maximize his profit.

Irvin, who has a business management degree from George Mason University, plans to close on his fourth short sale this month, a home in Fairfax County that is larger and pricier than any he has flipped so far. With low interest rates, scarce inventory, rising home prices and willing buyers around Washington, he doesn't plan on selling shoes again anytime soon.

 "There's always somebody who's going to want to buy your house," he said. "As long as there are short sales or foreclosures, I'm definitely going to want to be doing this."