Every client website has a shortcoming and it's in it's domain names. It's the standard that no two websites can ever have the same domain name, and save site extension name. so you may only need to check the URL and note suspicious ones.

For example https://www.facebook.com is different from https://www.facebook.online  or http://www.facebook.com and still different from https://www.fb.facebook.com, so if you can learn to identify the discrepancy in the domain names and you're 95% safe.