Dan Howell wrote:
Instagram: zero or low number of posts but following hundreds of people

Also IG:  names with numbers behind them...
Anyone with zero posts gets declined and blocked automatically.
Mine has a number, corresponding with my zip code, but I don't actively seek to expand my network.

GSmithPhoto wrote:
Also IG: 
Anyone with zero posts gets declined and blocked automatically.

might want to update that assumption since that will exclude legitimate users too for the last several years

much of Gen Z is only using the stories and the highlight reel these days, especially attractive women. its very common for people to have archived all of their photos, or started an account without any and don't plan to. should a model or someone seeking work leave something up? sure that would be more optimal for them but you can also consider being more flexible, or finding a different way to screen out people

Arizona Shoots wrote:
When receiving a friend request on Facebook or a new follower on Instagram, what are the key things you look for on their profile to determine whether or not it's a legitimate profile?

Me: I look for dog and cat photos.

On Facebook, first thing I do is look to see how many "friends" we share. Dog & cat pictures don't bother me.  Instead I check out their postings.  I'm usually the one sending a "friend" request, so I am suspicious of any one sending me one.  If it seems like there are a lot of ads for web products, it's a hard "no" from me. 

As for Instagram and "X" or whatever the nutcase owner calls his formally Twitter. I don't care anymore who follows me, I don't follow back unless they have a large number of followers themselves.  No way am I going to return a follow to the ones I see are scammers.  Some are fake accounts of real people, if I see that I report it.

Arizona Shoots wrote:
When receiving a friend request on Facebook or a new follower on Instagram, what are the key things you look for on their profile to determine whether or not it's a legitimate profile?

Me: I look for dog and cat photos.

One of the first clues for me if they have a number of images but no credited images or don't identify the photographer.