It can be hard since water sometimes travels along rafters and studs. I've seen it go several feet from point of entry to point of discharge. But it may be very simple to locate so I would find a reputable contractor to take a look at it.
Then the leak could possibly be coming from roof or attic by traveling down a wall stud. Or if it's against or near an outside wall then it may be coming from a leak in the siding. Also, do you know if the owner has done a disclosure on the property?
It depends what's up there....
1) A water supply line leaking from above bathroom or kitchen
2) The sewer line above leaking
3) The dishwasher leaking from the above kitchen, etc.
4) If along the outside wall, it could be water leaking in at the roof, or through the window.
Email me a pic if you need more help and the exact location of the leak on the ceiling.