If the IRS wants to spot large numbers of people who are stiffing the tax collectors, it might want to consider auditing a fast-growing segment of the mortgage market.New research suggests that more than 1 out of 6 borrowers who take out limited-documentation or no-documentation mortgages do so in part because they have significant under-the-table income that they do not report on federal tax filings.

Limited documentation and no-documentation mortgages once were used primarily by self-employed professionals, small-business owners and individuals who are heavily dependent on periodic bonuses or commissions. In limited or no-documentation programs, applicants typically state their income and assets to the loan officer but are not required to show detailed proof of that information for the lender’s files.

Interested in getting into one of the Hallinan buildings? Get in line. Because tenants stay for years, there’s often a waiting list.The most popular building, 801 Sutter St., has a waiting list several people long, said building manager Terri Price. “I can’t tell you how long the wait is, because you never know when someone will move out,” she said. “But I have people coming from Thailand and Taiwan who only want to live in this building.

“If you’re interested in a Hallinan building, I recommend any one of them. There isn’t one I wouldn’t live in.”

 Q: Do I understand correctly that it’s OK to stipulate in a lease that smoking isn’t allowed inside the rental premises, but it’s not OK to refuse to rent to smokers?

I have tenants who are smokers who apparently are conforming to the lease (which prohibits smoking inside), but are smoking outside and leaving cigarette butts on the ground outside the front and back doors, and in flower boxes, etc.

It remains to be seen whether they will clean them up when they move out. I would like to be able to deny tenancy to anyone who smokes, or at least prohibit smoking anywhere on the premises. Is this possible?

 Do borrowers really understand the pitfalls of mortgages with payments that can rocket higher after the first few years?

The answer is yes, according to Angelo Mozilo, chairman of Countrywide Financial Corp., the largest U.S. mortgage lender.

Advocacy groups fear lower-income borrowers are being stuck with mortgages that they can’t afford when teaser rates expire. And regulators recently required banks and thrifts to disclose more about “payment shock” when borrowers are allowed to defer some interest payments — until the mortgage adjusts and they wind up paying higher rates on a bigger balance than they started with.