I did something like this last year, only it involved rental cars. I had a one day trip to FLL, where I rented a Hertz car. I needed to be in SAN the next day, and I used my laptop to book another Hertz car; only, when I got to Hertz at SAN, I found out that I had booked my car for pickup at FLL. Fortunately, the nice Hertz people in SAN got me a car and honored the rate I would have had at FLL.