each scammer will have different signs that the person you are dealing with is a scammer. here's a great thread(that was created by Crypto Library) to analyse and find what signs/red flags you can look for when dealing with a scammer.

in the thread that I shared, you'll notice that the scammer asked for a favour out of nowhere, and he was asked to verify who he is, he gave a lame excuse so he won't need to confirm his identity. also, he brought his "colleague" to try and make Crypto Library feel pressured about the situation and when the "colleague" start telling about his situation he is trying to guilt trip Crypto Library into sending them the money.

the red flags you can find in this incident are the sudden asking for a favour that involves money, the giving a lame excuse to verify his identity, the trying to pressure Crypto Library by bringing in his colleague and trying to guilt trip Crypto Library with a sob story.