From an anonymous office in a New Delhi mall, matrimonial detective Bhavna Paliwal runs the rule over prospective husbands and wives - a booming industry in India, where younger generations are increasingly choosing love matches over arranged marriage.The tradition of partners being carefully selected by the two families remains hugely popular, but in a country where social customs are changing rapidly, more and more couples are making their own matches.So for some families, the first step when young lovers want to get married is not to call a priest or party planner but a sleuth like Paliwal with high-tech spy tools to investigate the prospective partner.Sheela, an office worker in New Delhi, said that when her daughter announced she wanted to marry her boyfriend, she immediately hired Paliwal.“I had a bad marriage,” said Sheela, whose name has been changed as her daughter remains unaware her fiance was spied on.“When my daughter said she’s in love, I wanted to support her - but not without proper checks.”Paliwal, 48, who founded her Tejas Detective Agency more than two decades ago, says business is better than ever.Her team handles around eight cases monthly.In one recent case - a client checking her prospective husband - Paliwal discovered a decimal point salary discrepancy.“The man said he earns around $70,700 annually,” Paliwal said. “We found out he was actually making $7,070.”It is discreet work. Paliwal’s office is tucked away in a city mall, with an innocuous sign board saying it houses an astrologer -- a service families often use to predict an auspicious wedding date.“Sometimes my clients also don’t want people to know they are meeting a detective,” she laughed.Hiring a detective can cost from $100-2,000, depending on the extent of surveillance needed.That is a small investment for families who splash out many times more on the wedding itself.It is not just worried parents trying to vet their prospective sons or daughters-in-law.Some want background checks on their future spouse - or, after marriage, to confirm a suspected affair.“It is a service to society,” said Sanjay Singh, a 51-year-old sleuth, who says his agency has handled “hundreds” of pre-matrimonial investigations this year alone.Private eye Akriti Khatri said around a quarter of cases at her Venus Detective Agency were pre-marriage checks.Arranged marriages binding two entire families together require a chain of checks before the couple even talk.That includes financial probes and, crucially, their status in India’s millennia-old caste hierarchy.Marriages breaking rigid caste or religious divisions can have deadly repercussions, sometimes resulting in so-called “honour” killings.In the past, such premarital checks were often done by family members, priests or professional matchmakers.But breakneck urbanisation in sprawling megacities has shaken social networks, challenging conventional ways of verifying marriage proposals.Arranged marriages now also happen online through matchmaking websites, or even dating apps.“Marriage proposals come on Tinder too,” added Singh.The job is not without its challenges.Layers of security in guarded modern apartment blocks mean it is often far harder for an agent to gain access to a property than older standalone homes.Singh said detectives had to rely on their charm to tell a “cock and bull story” to enter, saying his teams tread the grey zone between “legal and illegal”.But he stressed his agents operate on the right side of the law, ordering his teams to do “nothing unethical” while noting investigations often mean “somebody’s life is getting ruined”.Technology is on the side of the sleuths.Khatri has used tech developers to create an app for her agents to upload records directly online - leaving nothing on agents’ phones, in case they are caught.“This is safer for our team,” she said, adding it also helped them “get sharp results in less time and cost”.Surveillance tools starting at only a few dollars are readily available.Those include audio and video recording devices hidden in everyday items such as mosquito repellent socket devices, to more sophisticated magnetic GPS car trackers or tiny wearable cameras.The technology boom, Paliwal said, has put relationships under pressure.“The more hi-tech we become, the more problems we have in our lives,” she said.But she insisted that neither the technology nor the detectives should take the blame for exposing a cheat.“Such relationships would not have lasted anyway”, she said. “No relationship can work on the basis of lies.”