For ferreting out details on employment, finances and family history, cash bribes or bottles of whiskey work wonders, detectives say. Some admit hacking phones and computers and paying bribes to obtain credit card records.
Most premarital investigations are ordered by parents, although sometimes spouses-to-be want a little snooping done, including women keen to size up their prospective mothers-in-law in a society where it is common for couples to live with the husband's extended family.
According to detectives, investigations turn up significant problems in about 60% of cases. In about 10%, the discoveries are explosive enough — such as previously undisclosed marriages or serious hereditary diseases — to cause cancellation of the wedding.
For the caste-conscious, a hidden Dalit relative, or so-called untouchable, is also problematic. "Caste and dowries remain huge issues today, and people like to exaggerate," says Sachit Kumar, director of Globe Detective Agency.
A factor driving premarital investigations is the growing number of cases in which foreigners of Indian descent marry and then disappear, often taking huge dowries with them. It happens to 30,000 brides every year in northern Punjab state alone, according to India's National Commission for Women.
A woman named Priya, 35, hired detectives to investigate three potential husbands she met on matchmaking sites. The first one, it turned out, had lied about almost everything. The second was short-tempered to everyone but his mother, to whom he was slavish.
The third checked out on all counts. He's now her fiance.
"All told, I've spent $2,000 on investigations," says Priya, who asked to be identified by her first name only for fear of jeopardizing her marriage. "But otherwise I'd be trapped. It was money well spent."
Some, however, find spying on a future spouse questionable.
"There's no trust to begin with if you feel compelled to hire a detective," says Amrita O'Sullivan, 28, who works in an advertising agency in Gurgaon. "It's a complete intrusion."
After 30 minutes on the highway, the young woman in the silver Hyundai arrives at a suburban house, greets a man in a striped shirt and heads to the balcony for a cigarette.
"We suspect it's her boyfriend," scarless Kumar says over the whine of a power saw at a construction site. The detectives drive past the house, but they think the pair suspects something — further evidence of guilt, they say — so they retreat out of sight near the cul-de-sac's exit.
"I think he's a manager at her company," says Kumar-with-the-scar. "You develop a sixth sense."
The hours pass. It's over 100 degrees. A dog plunks down in the shade as the detectives listen to Bollywood tunes on a cellphone. Many people think private investigators are all about thrills, they say, but more often it's endless waiting.
There are minor compensations.
"Her eyes are beautiful," says Kumar-with-the-scar, looking at the woman's picture again. "It's always more interesting if they're beautiful. And in this business, beauty fuels temptation. Beauty has many takers."
Tanvi Sharma of The Times' New Delhi bureau contributed to this report.