A good rule of thumb: Don’t accept friend requests unless you know the person.
That doesn’t work all of the time, of course.
One way you can sort out evil requests from good ones, is to look at the requester’s Facebook page.
Are the photos snapshots or are they professional shots? Real people don’t post photos purchased from a stock photo site.
Photo situations: If you don’t personally know someone with a yacht, don’t accept a friend request from someone who has one. Look for photo situations similar to your own.
If you are unsure, message the friends you have in common with the requester to see if they really know them.