Why does the adjective in this case come prior to the noun:
Lisa est une très bonne vendeuse.
But in this case (also describing goodness or quality) it comes after:
Maurice est un professeur excellent.
Does this indicate that the BAGS guideline doesn't apply to the adjective excellent?
Here's a famous mnemonic tip to help you remember adjectives that come before the noun: you can call them the BAGS adjectives, which stand for
Beauty (joli/beau)
Age (vieux/jeune)
Goodness (gentil/méchant).