Do they ask for money?
If they ask for money then you should exercise extreme caution. Who would ask for money from a stranger? Think about it!
Are they in another country?
This may not be a problem. But sometimes it can be a sign of a scam if you are contacted first.
Do they make sense?
Maybe you send them letters and emails asking them questions. Do they answer your questions or do their replies seem to be generalised?
Guys: does she look like a model?
If your potential suitor looks like a model the chances are that a scammer is using a stolen photo and contacting you.
Ladies: did he fall in love with you amazingly quickly?
If the man seems to be falling in love very quickly and you haven’t even met in real life then this is a red flag.
Time is of no consequence
Just because you’ve been exchanging letters back and forth for 1 or 2 months doesn’t mean that you’re not corresponding with a scammer. These people do this for a living and time doesn’t matter to them.