Yup. Wasn't a genuine Sturgis contact as there was no record of him, and an EA was not going to waltz off and start showing houses to someone who had just rocked up, and who might be a timewaster without a bean to spend on a house.
So, perhaps a personal contact of SL's? - yet one whose contact details were never found in any diary. So we have no idea how she knew him or how she thought she could contact him. It's hard to see how a day-release lag like Cannan could have faked up a phone number so as to be contactable (I don't say it's impossible, just that it was hard. Maybe he gave out Superhire's phone number and got someone there to take messages?). So if a personal contact, one whom she couldn't actually contact. Very rum. The only thing I can think of that might explain that is if this was someone who had made advances to her but claimed to be "married and therefore you can never phone me". Cannan had actually been married and had a kid. So although this wasn't in fact why she couldn't call him, it's something he might have used to avoid giving her any number.
The train of thought some then proceed to is that given he can't have been a real Sturgis client or a personal contact of SJL's, he didn't exist, therefore there was no "12.45 37 Shorrolds O/S", and he was just a fake name prompted by the nearest set of For Sale particulars to her desk and her mate Herring, aka Kipper, who lived in that road.