The different categories of inspection deal with where the arborist is looking and how extensive the search for clues is. It's like detective work. A visual inspection. This is where the arborist will look for clues from the ground. A root collar exam.
Many trees topple because the roots are decayed.
An aerial inspection. The arborist will climb the tree to look for signs of weakness hidden from a ground inspection. Expect to be charged for a tree inspection. Root collar exams and aerial inspections take more time and skill so expect to pay more. A certified arborist has many years of experience.