As an estate agent (working for a different company), the system that we use for booking viewings and valuations classifies people into 4 different categories: 'Vendors' (people selling their property), 'landlords', 'sales applicants' and 'lettings applicants'. We take all of the same details for a number of reasons: 1. We ask all sales applicants (people who request a viewing/potential buyers) for their correspondence address - this is a security protocol so that we know who our agents are going to meet and where that person is from. The other reason is because the sales applicant may not have put their own house on the market yet and it may be an opportunity for us to suggest they consider us for a valuation. 2. We ask for their email address - this is so that we can send an email confirmation of the viewing that is booked. The number of times sales applicants call us to say, 'I thought the viewing was supposed to be at 3pm when it was actually 2pm....' If there is an email sent at the time of the booking, it helps our case to say that the time it was recorded in our system was 3pm and we sent an email to confirm it... Another way to think about it is this: If I was selling your house and I called you to tell you I had a viewer for you, you might want me to be able to tell you something about this viewer (have they got their own house on the market, are they a first time buyer, are they local....). If I said, 'I don't know, I didn't ask, I just have their name & number', you as a vendor would have good reason to be unimpressed and I would expect you to say. 'so it could be anyone then....even my curious neighbour'