How do you spot a fake keyholder before you get burned?

Came over from a couple of subreddits where the same scam stories keep popping up. Someone plays the confident keyholder, gets you invested, then asks for gift cards or a deposit to prove you are serious.

I do not want to be the next cautionary tale. What are the actual tells? I am guessing money is the big one, but I would love a fuller list from people who have been doing this a while. What made you walk away from someone who looked fine on paper?