Is it possible that if the celebrity is a jerk that they will come back and charge your $20,000 for having their quote on your website due to some bizarre legal do-dah I know nothing about?
The reason I ask this is what if (completely hypothetically, of course) a magician invented a trick and a famous magician bought it for a nice chunk of change.
The inventor was happy and put the celebrity's photo on his website.
Before the inventor ever got paid, the celebrity magician billed the inventor for the exact same amount the inventor was asking for his invention for promotional usage of his photo.
Without the legal team behind him, the inventor ends up with no money for his invention, afterall.
... that sort of thing.
Just to bee safe, I'd ask.