Domain assets (except for a small percentage of very liquid ones) are very difficult for people or robots to appraise with much precision.
I think the best way to view both appraisals (of the human kind) here or elsewhere, and automated machine ones such as Estibot, GoValue and NameWorth, is as a second opinion. By that, I mean first decide how worthwhile a domain name is based on criteria such as the value it would have to an end user, the potential pool of end users, past similar sales, the aesthetics of the name, etc. Do that before you ask for or get an appraisal - i.e. first make up your own mind after analytical work.
Then, after you have in your mind decided the relative worth of say 5 names you are considering, and perhaps a range of values for each, why not consult the automated tools to see if they confirm your opinion? They will along the way add information you might not have had (GoValue almost always does a good job with comparators and have sales not in NameBio, for example; while you can get the search/advertiser information in Estibot elsewhere, it is presented in a nice format, especially with the temporal graphs). If your opinion, and the opinion of others on NPs in appraisal thread or the automated worth estimates are very different, try to decide why. A second opinion is usually worth knowing, even if you don't think it is very accurate.
GoValue tends to appraise a huge number of coms in the $900 to $1900 range, so it may not be very discriminating.
Finally, even from the tiny sample of end users I have interacted with, at least in North America those who are seriously considering spending mid $$$ or more on a domain have probably stumbled on GoValue because GoDaddy is so big. So your potential buyers will know GV even if you disagree with it. I think that is why some well known names are angry with GoValue. I have sometimes picked up names even if I think the GV is way too low, but it is a negative to me, as it means potential buyers may well consult GD and think the domain should go cheap in those cases.
Bob