One of the most common techniques is to build up trust with the person by messaging for weeks or even months before suddenly having an emergency - the fake person being mugged but their daughter needing urgent surgery, for example - and asking for money.
But to dig deeper you need to look at the message content.
Here I’m going to walk you through the process of using Google Images to find out if the person might be using a fake photo.
Fake photos often point to fake profiles (or at least someone who’s lying about what they look like! Here I have a (fictional) profile where I’m a bit suspicious that I might be looking at someone using fake photos. Getting the Image Location from When logged into your account, open the suspicious profile and right-click the photo then: 2.
In many ways I’m writing this for men as I believe scams with beautiful women are aimed more at them (for obvious reasons).
That said, this should be helpful to anyone as there are multiple reasons people put up fake photos, not just for scams.