India, Oct. 1 -- Daniela De Pietri, a, a 50-year-old jewellery designer from Italy, landed in Delhi on Monday. Within hours, instead of heading to tourist destinations, she headed to the office of a senior Gurugram police officer, seeking help against a man she says had spent months convincing her that they were in a relationship, promising marriage and eventually persuading her to send him €900.

The money, she says, is no longer the point.

She has already spent twice that amount on flights, visa fees and hotels to travel to India and pursue a police complaint. What brought her across continents, she told investigators, was the emotional turmoil and sense of betrayal after she realised that the man she had trusted -- who introduce...