Do not trust automated domain name appraisal tools such as Estibot or GoDaddy’s Domain Name Value and Appraisal tool or any similar services.
Any domain name appraisal that is to be trusted requires an actual human domain name expert to perform the appraisal who knows what they are doing.
Automated appraisals are completely way off unless there is a sale of the exact domain searched and you are only given latest recorded price.
Similar domain sales in the past are not reflective of current or future value. Prices can go up and down over time depending on the domain name.
Often times automated appraisal tools don’t have sufficient data, they get confused and provide highly inaccurate results.
Because of their notorious inaccuracy and frequent under-valuing of domains, they actually hurt domain sellers.
The other side of the coin is that when domains are valued higher than market demand warrants it, it results in inexperienced domainers investing a lot of money in domains that will likely never sell for the valued price because of those automated valuations. This only serves to help the registrars.
For appraisals to be accurate within a reasonable margin of error, human intervention is a requisite along with good knowledge of the domain market and the industry the domain name is ideal for.