In Modern Supersymmetry, John Terning, on pgs 151, and 153 performs a so called 'reliable' instanton calculation when dealing with the ADS superpotential 'since the gauge group is completely broken'. Alternatively, see his slides #16, and 19 here.
My question has 2 parts, depending on the answer to the first part:
(1) What does he mean by 'reliable'? Is it a question of rigor?
Depending on the answer to (1):
(2) What is an example of an 'unreliable' instanton calculation? Is it back-of-the-envelope?