Using IRAC method

Cassie fantasizes about buying the ultimate smartphone by Kiwii Telecommunications, the KiwiiPhone XX Plus.  She works part-time while completing her bachelor’s degree in Business and saves all the money she can to fulfill her dream of having the Kiwii smartphone.  She has saved $1,900 so that she goes to the Kiwii Store one day before her birthday, and sees a stack of KiwiiPhones XX Plus with a big sign saying:

“Special Offer: Take your KiwiiPhone XX Plus for $1,600 only.”

Cassie can’t believe her eyes; this is the deal of a lifetime.  In a flash, she grabs a brand new KiwiiPhone XX Plus from the stack and sprints to the counter, all while telling her boyfriend about the unbelievable deal she just found.  She hands the KiwiiPhone over to the cashier before her boyfriend tells her that the KiwiiPhone XX Plus can be bought online from the Jungle website for $1,500 with insurance and 24-hour delivery.  Her boyfriend also admits buying her a KiwiiPhone XX Plus for her birthday the following day.

As the cashier scans the box of the KiwiiPhone, Cassie tells the cashier:

“I am very sorry, I changed my mind. I am not taking the KiwiiPhone XX Plus home.”

The cashier then responds:

“I am afraid it is too late.  You took this item from the stack; now it is yours.  You are bound by a contract. If you don’t hand over the cash, I will have to call the police.”

Is the cashier correct?  Is there an agreement between Cassie and the Kiwii Store for a $1,600 KiwiiPhone XX Plus?