What's surprising about this trend is that women are spending money on these "investigations" even during the dating stage of a relationship. While it may be necessary for married women to go through the hassle of paying for a PI report in order to prove adultery and get a divorce, unmarried women can simply, well, walk out of a relationship.

After all, the services of a PI don't come cheap. John Lee, a PI with Ranger Investigation and Security Services, estimates that the market rate for a PI is between $100 and $200 per hour. A typical case, stretching over a few days, could cost between $3000 and $10,000 and even more if travelling is involved. For instance, a four-day assignment to Thailand could cost $40,000.

A Her World straw poll of 20 women revealed mixed views, with half saying it's never okay to get a PI to check on one's partner. "If you suspect him of something, wouldn't it be easier to ask him directly? asks Gong Pan Pan, 26, an arts manager. "if you don't trust him, you should just leave. The only reason for hiring a PI it that you lack courage and need someone to tell you what you already suspect."

So why are women doing this? The most common reason is to avoid a bad match for a lifetime.

Most PIs add that their clients are usually women considering marriage - those who are engaged or about to get an HDB flat. They usually hire a PI due to a "trigger" - an unexplained change in their boyfriend's personality or behaviour - which made them suspect something was wrong.

"What they're paying for, essentially, is peace of mind - a sense of security before going into marriage," explains Richard.

One of his clients, Alexis, paid almost $18,000 last year for this "peace of mind". The 27-year-old systems analyst, who declined to be reveal her surname, had been engaged to a man she'd dated for four years. Seven months into their engagement she noticed that he was increasingly distracted when they were out together and was constantly SMS-ing someone "about work".

"I knew intuitively that something was wrong, and even confronted him about three times. But he always denied it," she says.

A frustrated Alexis engaged two PI firms, including Richard's, to confirm her suspicions. The first charged her $10,000 for three day's work, but was unable to find anything suspicious. Undeterred, she paid Richard about $8,000 over five days, and managed to get photos and videos of her fiance bringing an unknown woman back to his apartment.

She spent a week collecting her emotions before confronting him with the PI's report. Her fiance was stunned and angry that she'd gone behind his back. "But he couldn't deny it any longer with the evidence in his face," says Alexis, who is now happily engaged to another man. She says her ex dated the other woman for a while before the relationship fizzled out.

She has no regrets about hiring a PI. "My ex said that he would stop cheating once we got married. But I believe that once a cheater, always a cheater/ It's better to know now than to get a divorce later on, especially if there are children involved," she says.

But she won't subject her current beau to a background check - the process of engaging a PI and waiting for the investigation results is too physically and emotionally draining. If he were to act suspiciously, she says she'd simply ask him whats up. "But so far, he hasn't given me any reason to suspect him," she says.