I'm a private investigator – these are the telltale signs that your partner is cheating

Yahoo

12-08-2025

Ali Marsh is an expert in human behaviour, thanks to her unusual career as a private investigator.
Now 58, she's been working as a PI for nearly 10 years – and in that time she's taken on a host of cases, from looking for missing people and tracking down family relatives to debt recovery and identifying cheating spouses.
Previously a worker in the care industry, Marsh, who lives in Oxfordshire with her retired husband and has a grown-up daughter, says: 'I've got the skills as a listener, picking up on people's vulnerabilities and body language. I am quite perceptive and have learnt to adapt to different personalities.'
Her startling career change came after she was mugged at knifepoint. While she was waiting for a bus after a night out, a man approached her and demanded that she give him her bag. Something snapped. Not only did Marsh fight back, she chased the mugger too.
'I was so angry that he thought he could do that,' she says. 'I started to chase him and he was so surprised.' At the time, she had been grieving the loss of her father. 'I was destroyed by his death,' she says. 'That [the attempted mugging] was the pivot for me to change my life.'
She wanted to know why people committed crime, and went on to study psychology and criminology at the Open University. She then moved on to profiling, looking at ways to identify suspects.
And at the age of 50, she became a private investigator, setting up her own agency, Miss A.M. Investigations. She charges £85 per hour but, if a case could be drawn over days or weeks, will negotiate a total fee.
Since then, she has taken on a host of cases – a number of which are outlined in her new book, Private Lies. She says over the years she has come to understand how cheaters work. So what are the telltale signs?
How to spot a cheater
Emotional and behavioural shifts are one clue, she says, explaining: 'They become distant, there are changes in intimacy and a lack of interest in you as a partner.' Look out for them withdrawing from you and not engaging physically or mentally.
'They also change their phone or passwords and leave the room when on the phone. They have a sudden interest in their own appearance – they lose weight and start going to the gym.' Check if there is a change of hairstyle, a new fragrance or aftershave, or new clothes. 'There are sudden, unexplained expenses,' says Marsh – not to mention absences.
In one scenario, she was following a man who had told his wife he often had to go away because of work. His wife had noticed a change in him, became suspicious, and believed he was cheating. After hours of surveillance, Marsh got pictures of him kissing the other woman at her front door. Case closed.
'People are devastated when they find out, but often I think they know,' she says. 'They just want me to confirm or deny. And I've had men as often as women coming to me. It isn't just a man who cheats.'
On another occasion, she managed to unmask a coercive, controlling husband who was cheating with a younger woman. Not only that, he also had a secret business, hiding his wealth, which Marsh tracked down. Her discovery helped the woman financially when it came to their divorce.
'I punched the air with that one,' she says. 'He was really horrible and she was lovely. I do think that is why I do this.'
Another sign to look out for if someone is straying is whether they are talking about someone a lot. 'If they have fallen for someone at work, they may mention them often,' says Marsh. 'They want to talk about them but they can't, so they say 'so and so did this today'.'
And they will start going out more. 'They can cause arguments, giving them an excuse to storm off – 'I've had enough of this, I'm off out',' she adds.
How to spot a catfisher
Infidelity is one thing – but what if your beloved isn't actually really in love with you, but with your wallet?
There have been numerous cases of both men and women falling for catfishers and scammers who use fake photos and online personas to lure people into relationships – an increasing risk in a world in which online dating is normal. 'People work on these scams for a long time. They vet people to get to the right person,' says Marsh.
But there are steps you can take to protect yourself.
'Scammers are skilled at getting into your head and preying on any weakness,' says Marsh. 'If they send you any images, do a reverse image search.' You copy and paste the image into a search engine, click search, and the results will show whether it has been used elsewhere.
'Ask yourself if the image is legitimate, as fraudsters often use stock images or other people's,' she adds. 'I did a reverse image search for a friend recently. She was going out with someone who was slightly strange.
'He phoned her up and said he had been in a really bad crash, so could she send him some money so he could go to a garage. I did a reverse search, and the photo he had sent was of a car crash that happened two years ago.'
Other telltale signs include if they mirror your hobbies or life experiences, pretending they like the same things you do, whether that's squash or opera, football or theatre. 'They don't really offer a lot about themselves or what they do until they know what you like,' says Marsh.
In another of her cases, a man called Bradley* had been catfished on a dating app by someone called Alfie*. He had love-bombed Bradley, showing that they had similar tastes in music, a love of Japanese food and shared family values. Then Alfie said his mother was ill and he needed £150 for the train ticket to visit her, which Bradley sent. Alfie then disappeared – a textbook case.
Marsh discovered the deception by trawling through images online and realising the Alfie in question did exist, and had a girlfriend in Essex.
'How cruel is that?,' she says. 'You get to know them and supposedly trust them and think 'this is the person for me'. That someone would do that and still get money out of you. It wasn't thousands, it was just £150, but even so.'
Other signs of a catfisher are, she says, 'if they won't speak to you via FaceTime, only via audio. They'll say they can't get FaceTime on their phone. Or they will always cancel at the last minute when you are going to meet, particularly citing family issues or health reasons'.
Another good pointer is their social media profile, whether that's on Instagram or Facebook. If they have a lot of followers and little engagement, it's likely to be fake. Check, too, if they tag lots of people, which could be a giveaway.
Marsh says she is particularly concerned about scammers preying on the elderly and, with advances in technology, their scams are getting far more sophisticated. 'When I go and see elderly people, I say to them don't answer the phone to them, don't give them what they want. Don't give them your address.'
How to catch a cheater out
Marsh uses all sorts of methods to get to the truth and says her biggest assets are 'instinct and a dog lead'. She often uses the guise of a dog walker to get talking to people, or has 'lost' cat pictures on her phone. 'Then I can say 'can I look in your garden for my lost cat?' and get through the house.'
She also has personas with names such as Susan and Claudia. On one occasion, she joined a book club to check on a woman whose husband thought she was cheating.
'My personas are always based on someone I know, so I have got a story. It's more credible that way,' she says. And she can change her look by dyeing her hair or wearing different glasses. She also has a profile of her own on a dating app so that she can check whether people she is investigating are on it.
Her other equipment is a long lens camera, a Dictaphone, a notebook and a strong constitution. 'Sitting in cars for hours at a time on surveillance, I think I have got the bladder of an elephant,' she says. 'You have to be alert, waiting for people to move. It's mentally tiring rather than physically.'
Marsh also feels that being a woman, and an older woman, has helped.
'Some people say you feel invisible at this age,' she says. 'I wouldn't say I do. But if you saw me in a car, you wouldn't think 'oh, she is following me', you would think 'oh Christ, she can't work out her sat nav!' It can sometimes work to your advantage.
'Women are good as private investigators because we adapt well to people and circumstances, whereas men can be a bit awkward if they are not in any kind of familiar territory. Patience is a big factor in my job.'
Keeping safe while on surveillance
What about her own safety? Has she ever been bothered while on surveillance? 'Not often. I keep a load of flyers in my front seat, so if someone taps on the window, I'll say 'oh, I was just dropping these off'.'
She also has an amicable relationship with the police. 'If I was going to be doing surveillance for a long time in one place, it is always useful to go to them and say 'this is why I am here'. So if people phone up and say there is a strange woman in a car, they know.'
How does Marsh switch off? ' I love watching real crime,' she laughs. 'But not violence. I like a nice cosy one, I love Richard Osman.'
And despite all the scamming, cheating, catfishing and resultant heartache she has seen, she still has faith in human nature. 'I think inherently there are more good people than bad.'
Private Lies: True Stories From My Life As A Private Investigator by Ali Marsh is out now, £20, Blink, Bonnier Books UK
*Names have been changed
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