If all goes well on the phone you will probably be offered a one week trial. It is very rare for people to fail the trial period, but if you do not like the job you are obviously free to leave. You can call Dee every day until you find work. Dee receives in new job requests every day, so there is always something new. However you travel there is normally somewhere to place you.
Single travellers are very easy to place.
Groups of more than three are a little harder but can normally be placed in nearby hotels.