In my time we used to have to buy a news paper for the classified ads. I’m aging myself here.
Now days everything is digital. The use of free ads has its attributes. However, it’s also attracts scammers because it’s easy and free to make an account. These bad actors use these ads to get your email address. Once they have that they are only one step away from getting into your account.
Hello, I’m listing this ad for my aunt/ uncle, mother inlaw etc. Please contact them at email@example.com.
The simple solution is don’t answer by emailing them back. Report the ad to Facebook and move on. They aren’t really selling a new Harley for $800.