John knows that Susan has coveted his classic car for quite some time. Finally willing to sell it, he sends a letter to Susan offering to sell the car for $15,000. Susan responds by saying she needs time to arrange financing. Susan offers John $100 to keep the offer open for two weeks. John agrees, taking the $100. Three days later, Roberta contacts John saying she is interested in buying the car and has the cash to buy it outright. John is concerned that if he doesn't sell the car to Roberta now, she may not be interested later. Furthermore, Susan may never be able to arrange financing. John is afraid he may end up with no buyer at all