They can see how many times a property has been viewed on line. As a listing agent, I can see how many people have viewed my listing versus the average number of "hits" in that town. I think popularity is a relative term when it comes to real estate. The first factor is the style, condition and location of a property of which these search engines cannot give you an indication, rather an agent can guide you to the more "desirable" locations, convenient locations etc. A house could show as house beautiful on line but then you find its next door to the dump! I hope this help, and good luck in your search.