Rey knows that Amelia has coveted his classic car for quite some time. Finally willing to sell it, he sends a letter to Amelia offering to sell her the car for $65,000. Amelia responds by saying she needs time to arrange financing. Amelia offers Rey $500 to keep the offer open to her for two weeks. Rey agrees, taking the $500.

Three days later, Katilyn contacts Rey saying she is interested in buying the car and has the cash to buy it outright. Rey is concerned that if he doesn't sell the car to Katilyn now, she may not be interested later. Furthermore, Amelia may never be able to arrange financing. Rey is afraid he may end up with no buyer at all.

He asks for your opinion.

What do you advise and why? What is the legal basis for your answer?