daveslutzkin, the average user of estibot type tools may use the Flippa tool and attach some credibility to the results. There might even be some chatter like "Wow, see how much my site is worth!"
But without disclosing the methodology/calculation behind the valuations the tool won't cut it for experienced users. For all they know, you could be basing results on something simplistic like PR or Alexa rank, or backlinks or number of letters in the domain name or a random number generator. Telling us there's a complex calculation happening in the background without telling us what that calculation is would leave suspicious buyers (and sellers) with more questions than answers - questions about your methods and questions about your intentions.
That's true. That's why it's important to be open with the users of the tool and tell them how the calculation is being done so they can make allowances for areas where the tool has flaws. It would also fuel suggestions from knowledgeable users on improvements that could be made.On a more cynical note, I'd imagine if it gave a default range of $0-200 for every site entered, then that probably would be 90% accurate for sites that are listed on Flippa