Can you explain how to get the correct answer to this question?

As the owner of an art gallery with a keen eye for upcoming talent, you find a painting that you feel is sure to net a large profit from a relatively unknown artist. You contact the artist and negotiate to privately purchase the piece for $5,000, which you believe will be worth at least $25,000 in the next five years. A contract is signed to purchase the painting which is to be delivered to your gallery. Realizing that you are the successful owner of an art gallery, the artist feels that perhaps he sold the painting for too low of a price and returns the $5,000 check to you instead of delivering the painting. How should you proceed?