Call it a tale of two real estate markets.

While sales are slower in the posh downtown Boston condo market, prices continue to remain sturdy. The median price for luxury condos in the city actually jumped last year by nearly 10 percent to $730,000, global financial crisis and all.

But while all eyes are on the glitzy downtown market, few are paying attention to another story as crucial, and maybe even more, for the Hub’s long-term health.

Things looked pretty rosy as well just as couple years ago in the sprawling working class enclaves of Dorchester and Roxbury. While far from the gleaming luxury towers downtown, triple-deckers were fetching $500,000 or more, while the newly converted condo units inside were selling for $300,000 or more.

Many of those very same Dorchester condos can now be had for anywhere from $25,000 to $75,000, having been foreclosed and now put on the block by their lenders, notes John Anderson, a Dorchester housing researcher who has tracked more than one real estate boom and bust over the years in Boston’s inner-city neighborhoods.

As many as 1,500 homes and condos have been foreclosed on in Dorchester, Roxbury and Mattapan over the past three years as the real estate market went south, he estimates.

“Those numbers are not coming back anytime soon,’’ said Anderson of the boom times when Dorchester triple-decker condos were fetching $300,000.

The False Boom

Still, when prices were rising across the city, few were complaining. It seemed like the miraculous real estate wealth machine was raining money on rich and poor alike.

But in the city’s poorest neighborhoods, it was a false boom, driven by unscrupulous small-time speculators and a flood of ridiculously easy-to-get subprime mortgages that invariably slid into foreclosure.

Sob stories about naïve buyers who got conned into buying homes they couldn’t afford are now a staple of the housing downturn.

Yet few understand how much outright real estate fraud drove prices upward – that is before they came crashing down in now foreclosure battered Roxbury, Mattapan and Dorchester, Anderson contends.

And having reported on more than a few such deals myself over the years, I tend to agree.

While there certainly were more than a few people who got conned, there were also many deals in which real estate scammers simply recruited straw buyers to concoct phony sales. Mostly small-time speculators, they would dream up juicy prices for condos in Dorchester or other working-class neighborhoods that no real buyer would pay and then kick back, say $10,000, to some clueless or corrupt fool for signing his or her name on the mortgage paperwork.

The real crime was that it really was that simple. In their glory days, the subprime companies were all about loan volume, with the worst having few quality controls. You could make up any job or income you wanted on the now infamous no-doc mortgages, long since labeled “liar loans.”

It’s not hard to figure out which homes were sold to straws and which to struggling and often duped buyers. The really bad stuff would start to go bad almost immediately, with foreclosure proceedings kicking in a few months after the condo in question had sold.

‘Making Up The Numbers’

Given foreclosures take months to work out, no payments were likely ever made on some of these units. There was never a real homeowner out there behind the loan to actually move in.

“They were never worth that much to begin with,” Anderson said. “They were just making up the numbers.”

But the big picture is even more disturbing. While as bad as the foreclosure crisis has been in Boston, you can find similar distress in poor neighborhoods and rundown industrial cities across the country. And that’s before you get into the massive foreclosures in new condo high-rises and housing developments in myriad cities across the Sun Belt.

All told, it is a fraud that dwarfs anything – even Bernie Madoff’s stunning $50 billion Ponzi scheme. Hundreds of billions, at least, of home and condo values were lost in dreary foreclosures.

“If this is replicated in every city in the country, it makes Bernie Madoff look like an amateur,” Anderson said.

While that’s shocking enough, the really sad thing is this whole boom and bust cycle is poised to start all over again back in Dorchester and other neighborhoods. Armed with cash, the speculators are back, scooping up many of these distressed units, contends Anderson, who has spent years tracking real estate trends in Dorchester Roxbury and Mattapan.

The new owners will hang onto these units for now, renting them out until the next upswing in prices. Then you will see a surge in condo conversions, with enough phony sales mixed in to send prices through the roof. The vast array of subprime lenders that helped pave the last road to ruin are gone, but believe me, something and somebody else will replace them.

“I would say 60 [percent] to 70 percent of the condos on the market are foreclosures,” Anderson said. “They are almost universally being bought by investors, with cash.”

Still, this is hardly the first bust like this in Boston’s poorest neighborhoods. Rather, it’s part of a boom-and-bust cycle spanning decades, with a similar shakeout happening back in the early 1990s.

It’s an issue that Anderson, and maybe one or two other local housing experts, has been talking about for years. Of course, no one has paid them much attention, either.

Pushing The Pols

The real question is whether the current downturn has been painful enough to force city and state officials to get their heads out of the sand and start looking at how to halt this vicious cycle.

So far, there has been a lot of political hot air and mainly symbolic efforts to turn around Dorchester’s Hendry Street, which, despite its cluster of foreclosed homes, is just the tip of the iceberg.

But Anderson, an up-from-the-bootstraps housing expert who built his own foreclosure database and made a living doing appraisals for banks, won’t be around much longer to pester city officials.

After more than three decades living in Dorchester, Anderson and his wife have sold their beautiful old Victorian and are preparing to move to Florida.

Not a bad place to land for a guy who gets his kicks out of tracking down housing fraud.