Domain appraisal is appraising the value of domain name. There are many ways to do this, but there is no 100% accurate appraisal. Domain appraisal could be free or paid. Domain appraisals could be used if you are curious about the value of your domain, but don’t take them too serious.
The real value of domain name is almost impossible to determine with accuracy. Some types of domains have minimum value and you can’t get them beyond that value. Here I mean on LLL.com, quad premium LLLL.com, CCC.com etc... They have minimum value, but not maximum as someone would pay $xx.xxx for CCC.com, and someone would not pay more than $5000 for LLL.com with all premium letters.
I sold many domains for $x.xxx which had appraisal of $0 to low $xx. Also, I sold many domains for $xxx which had appraisal in high $x.xxx range.
It is not easy to get accurate appraisal, so it is best that you do not ask for it at all. Try to get for your domain as much as you can and do not care about appraisal.