Mary is organizing the end-of-year party for her workplace. She hires a function room and pays a 10% nonrefundable deposit, with the remainder payable on the day. She also hires Seth, a popular local DJ to perform for 6 hours that evening for $1000.00.

One week before the party, Seth contacts Mary and informs her that he cannot perform at her event because he already had a booking for that evening, which he had forgotten about at the time. Mary is desperate for Seth to perform because she does not think she will be able to find a replacement and will lose the deposit on the function room if she is forced to cancel. She offers Seth an additional $500.00

on top of the $1000.00 already agreed to if Seth will perform at her event. Seth eventually agrees. Seth appears as promised and performs to a rousing reception for 6 hours as agreed. At the end of the evening, Jill pays Seth $1000.00. Seth complains, saying that Jill promised him an extra $500.00 and that he canceled the other booking in favor of her event. Jill tells Seth that it is not her fault that he double booked himself and that as they had an agreement that he would be paid $1000.00 for his services, she was not obliged to pay him anything more

Advise Seth whether he is legally entitled to the $500.00.