how do i know when some is tying to scam me online
If you are referring a person, it would be very hard to identify. But if certain company or organization is doing this, you can find out via the reviews available though a simply google search and analysis.
As an example if company is ‘ABC’, you can find out their actual details by searching for ‘ABC reviews’, ‘ABC legit or scam’. There will be lots of review points and it will help to find out a solution for you.