You can follow domain sales each week to get an idea what is selling and for how much.
http://dnjournal.com/domainsales.htm
Looks like FootFetish.XXX went for $89,000
Since the domain in question was asking for $6500, drop down to the section "Additional Sedo .com Sales Between $2,000 - $6,000" and see what kind of names are being sold there. How does the name you want compare to these?