For example, the assigned model is Macan. The shopper can call the PC and say something like: “I heard there is a new model of Macan, I am very interested, how much is it? Do you have any in your PC?”
Then normally the SE will use this chance to offer you an appointment. If the SE offers you an appointment, the shopper can take it or suggest another date.
If the SE tells the shopper that he can come to the PC at any time, the shopper can say “ok, then I will come over tomorrow (or another certain date).