Then, over a single noisy, dusty weekend, hundreds of shoppers - attracted by rock-bottom prices, and by the unique patina and provenance of the goods they find - pry up and cart away by the following Monday just about everything worth saving.
At the most recent sale, Christine and Jim Wilson, who are renovating their house in Paoli with salvaged materials, arrived early and were rewarded with a flagstone retaining wall for $100. (They wanted the matching patio, but a couple from Claymont, Del., beat them to it.)
"We're saving hundreds, I would say," said Christine, who had searched for a stone wall on Craigslist, which was unsuccessful, and at Home Depot, which was expensive. "Plus, I like the 'green' aspect. That's my favorite part about these sales, is not seeing nice architectural details and things end up in landfill. If you go to Home Depot, you're not going to get things with character like this."
The couple had attended five or six of Tobin's sales, but the stone wall was their first purchase. It was a victory that would mean hours of backbreaking work. Jim began pacing the driveway, making calls on his cellphone, scrambling to borrow a truck and perhaps an able-bodied friend or two.
Tobin, who has a stall at Resellers Consignment Gallery, a marketplace in Frazer, has 3,200 people on his e-mail list, and knows many of them by name. Regulars know that sales start at 9 a.m. sharp, and line up early if they're on the hunt for an especially hot item. Every attendee signs a waiver and is assigned a number. To buy something, the shopper marks it "sold" and notes his or her number, then pays and begins removal.
Tobin has refined this process over nearly three decades in business, picking over old Main Line estates, disused churches, and, once, a block of seven houses taken by eminent domain for highway expansion.
The enterprise was born about 25 years ago and stemmed from Tobin's interest in architectural antiques, he said.
"A builder down on the Main Line called me and told me there was some stuff in this house that they were going to tear down, and that maybe I'd be interested."
When Tobin realized there were too many treasures to cart away, he told the developer, " 'You should have a sale in that house.' And he said, 'No, you should have a sale in that house.' "
Tobin took him up on that - and as more old Main Line estates were torn down and replaced by five- or six-home developments, his business flourished. As newly arrived immigrants, Tobin's own grandparents had been caretakers for such an estate, but he said those mansions represent a bygone era.
"Some people say, 'Oh my God, it's horrible that they're tearing those houses down.' But the truth is, people can afford to buy those houses, but they can't afford to maintain them."
Sometimes, though, long-ago owners return to salvage fragments of their past. One woman learned at the last minute that her grandfather's house in Media was being demolished - and caught a flight from Atlanta that day to pry up a doorjamb marked with a family growth chart.
It's a sporadic business: Tobin said the number of sales varies from year to year making it tough to give an estimate. The business grew by word of mouth over several decades - driven by the transformation of a Main Line of old country estates into denser suburban communities, and by a growing interest in salvaging the fine details of those doomed mansions - but slowed in the recession as tight credit and a sluggish new-housing market discouraged development.
Tobin wouldn't disclose how much his sales typically generate or what his own cut is, but pointed to a Tudor-style mansion that he sold for parts in 2000 before it was leveled to make way for the Radnor Elementary School. Tobin said the superintendent estimated that the school district, which had been considering organizing its own, in-house pre-demolition sale, had more than doubled its take by using his service.
The biggest-ticket items tend to be whole kitchens; Tobin once received $40,000 for a large kitchen stocked with Sub-Zero appliances and high-end cabinets. And certain houses can be expected to offer more luxury - the former Main Line home of Julius Erving, basketball's Dr. J, for example, or the mansion of John Eleuthere duPont, the Newtown Square multimillionaire and philanthropist who was convicted of murder in 1997.
The sale in June, though, was nothing so lavish.
"They're just tearing it down and building a new house," Tobin said. "It's standard operating procedure."
The crowd was split between do-it-yourselfers and professional rehabbers.
Sandy Elicker of Wynnewood knows to bring tools, a shovel, and tarps to each sale.
"I didn't come as prepared as I should've at the beginning," she said. "Now I know better."
In the last nine years, she's bought built-in cabinets, planters, sinks, and shrubs. This time, she left with a metal shelving unit.
Brian Walheim purchased all the oak flooring in the house, and planned to start the removal in an upstairs bedroom and work his way down, working around the other shoppers. The Berwyn rehabber said that he looks for used fixtures to install in rental units where it doesn't pay to install new items; the unique, higher-end finds can add value to his investment properties.
Elizabeth McLaughlin and Suzanne Stuut, business partners from Radnor who renovate old Main Line houses one at a time, said they're attracted by the age of many of the houses being dismantled. At one sale, they purchased hardwood floors and an entire kitchen from Tobin. "The house we redid was 100 years old, and the floor we put in was also 100 years old, so it matched," Stuut said.
Anyone older than 13 is welcome at the sale - kids aren't allowed, since it's an active demolition site. However, Tobin said he's observed some dangerously slapstick moments among DIY rehabbers in over their heads. Those in too deep can hire one of his workers to help with demolition or moving. Some high school students work for $10 an hour, but others are more experienced and charge more, Tobin said.
For first-timers like Ellen Bugary, the experience can be daunting. Bugary had come from Philly to look for wainscoting for her dining room. She didn't find exactly what she was looking for, but said she'd be back next time. Still, she thought that the bargain-hunting was bittersweet.
"Why would they want to tear this down?" she asked a friend, lingering in the airy master bedroom. "This is too nice."
For information on pre-demolition sales, including how to get on Tobin's e-mail list, go to www.predemolitionsales.com.