Most I've experienced will ask for about twice their slot money, then come back and ask for more, but eventually sign. For instance,
Donatello Brown was "May sign if the deal is right." He asked for $6,000,000 originally, came back with $8,000,000.
But there are some that don't sign. Probably 75/25 to 80/20, something around there, on those that sign/don't sign. Just pulled those numbers out of the air, though, based on how it feels from past experience.