John had just started a business selling smartphone accessories. He had his stall set up in the city where his stall had displayed all his goods for sale. One Friday, Jill, upon visiting Johnâ€™s stall found a portable charger she needs for her smartphone and asked for the price to which John responded that it cost $20. She then replied,â€ OK, but currently, I do not have the cash with me but I will come by on Tuesday to pick it up.â€ John responded was â€œDonâ€™t worry; I will be here every day next week.â€
On Tuesday, Jill goes up to John and says, â€œThis is $20 dollars for the portable charger.â€ However to her disbelief, John told her that the price has increased to $30 over the weekend and that he would not sell it to her at the previous price of $20.â€
Advise Jill whether she is able to legally force John to sell the charger at $20.