Automatically generated script appraisals are useless. Appraising a domain name is a quite complex process, which can only be done accurately by an experienced domain appraiser. However, even then it is sometimes difficult to determine a realistic value for a domain name. I have already tested appraisals from all major companies and I must say Sedo's appraisals are good relatively often, but Afternic appraisals are crap (my personal opinion).
If you want to get a free appraisal forget about those free appraisal scripts. Just post your appraisal request here at DNF and I'm sure you will get some good opinions on your domain name's value.
Otherwise, if you are looking for an official written appraisal go to a reputable domain broker.