Would you patron an artist who didn't make you look your best? Personally, I'd want my money's worth.
A skilled artist could remove quite a lot of imperfections.
The portrait of the younger Lord Byron, painted by Elisabeth Vigee-Le Brun, may be an instance where the artist changed her subject a bit. However, the early picture of the poet is not an example of the artist's best work either.
Vigee-Le Brun was extremely skilled and prolific, however. She was also a favorite of Marie Antionette and did many portraits of her.