Why, Sometimes, I Get A Strange Domain Appraisal Message ?

[blue crystal]

Sometimes, I get this message “SORRY, WE ARE UNABLE TO PROVIDE A RESULT FOR THE DOMAIN NAME YOU PROVIDED.” when I ask for the appraisal of some very good name like, for instance, “bestbuy.com”.
However, upon searching through google I found out that there was already a site with this domain name.

Why is that ?