I think I know the answer to this, and my guess is "No", but I don't have a definitive reason what that guess is.
When you see on the cover of a book, not from a newspaper or reviewer, but from another author, something like:
"Gene Wolfe is so good he leaves me speechless."
- Ursula Leguin
Did she get paid for this, did she write this somewhere in a public forum, or was it just a verbal quote taken down.
This is a question about novels in general, but applies to SF & Fantasy as well.