How Would You Determine The Difficulty Of Getting Into A Specific GMB 3-Pack Listing?

In episode 183 of the weekly Hump Day Hangouts by Semantic Mastery, one viewer asked how one can determine how difficult it would be to get into a specific GMB 3-Pack.

The exact question was:

Hi Guys,

Thank you VERY much again for your help here on Hump-Days. Hopefully I'll be able to somehow return the favor at a future time

Other than the typical things, what would one look at to figure out in advance whether a specific GMB 3-Pack was very difficult or very easy to get into, and how would you determine where on the difficulty scale it was between those two opposite ends on the spectrum?

Thanks a lot

Gordon