If the average of IVs is ~30 he'll say the pokemon has outstanding potential
average is ~25, relatively superior potential
average is ~20, above average potential
average is ~15 or below, decent potential
He'll also say which stat has the highest IV. If the pokemon has multiple stats of that value, he'll say one of those stats in random
If the value of the highest stat = 31, he says "it can't be better in that regard"
value of highest stat = ~30, "fantastic in that regard"
value of highest stat = ~20-25, "very good..."
value of highest stat = ~15 and below, "rather decent..."