These statistics are very difficult to collect. So ideally, appraisal firms should share their sales databases. More realistically, new firms will appear specializing in collecting, collating and selling domain sales information. There is an obvious economic temptation to minimize the use of people in the appraisal process and maximize the use of appraisal 'algorithms'. In this author's opinion, appraising domain names will always be a job for humans, with just a supporting role for technology.
Domain names are examples of 'natural language'.
No computer algorithm has ever come close to understanding natural language and its infinite subtleties. In the main, any attempt to replace people with programs will lead to highly inaccurate and sometimes embarrassing valuations. Ideally, they should have some professional qualifications or at least some real experience in the fields in which they specialize. Again, some degree of specialization looks to be the appropriate answer. It should be obvious that appraisal firms should aim to be a neutral party sitting between buyers and sellers.