I also go by the followers/follow > 1, but for N>500. If a friend of mine follows 100 people but only has 50 followers, I give them a pass. I'll flat out block someone if it's clearly a "social media expert" with follows close to followers over 1000. It's pretty clear that they aren't really following anyone and will unfollow me in 48 hours if I don't help pad their stats.