How to handle "wait and watch" type customers?

I am involved in a Housing rental listings project where users are given a number of choices to choose their preferred home from. All choices fulfill their original criteria(Budget for rent, location, area etc.). Though they say they have found their perfect home, yet they just wait and watch for better listings. Later on, when the listing is gone, they want to get it back.

We have tried a handful of solutions like -

• sending regular emails, notifications stating that the listing is available for a limited time.
• Making calls to remind them that they may lose this opportunity. When we ask them why they are not going for a particular listing, their response is "I like this house but I'll make my decision after some time".

But none of them seems to work. We want to understand the core of this mentality. We understand that this is not a unique problem and multiple variations of the same problem exist in other industries also.

Has anyone done an extensive study on this kind of behaviour?