Just a followup to add that Go Daddy won't release that info if the domain is
using their WHOIS privacy service.
True but, if a letter is sent though the email address listed and the physical address listed (I'd say send it with tracking - FedEx overnight etc..) then GoDaddy should forward it to the registrant and forward the mail to the registrant (and billing the registrant for the mail forward).
I'd say it is a good time for a letter from a lawyer. Private registration can be looked upon that the registrant is hiding something and his offer to sell it to you for $5,000 shows that it was registered in bad faith.
To be sure, he contacted your company first about selling it, you didn't contact him, correct?
Edit:
Well for one, I am a licensed Nissan franchise so yes, I am permited to use the domain. As far as the dba, I was not involved with the store at the time it opened but even if I was, the name of the business was more important than the domain name I'm sure. (or maybe they didn't check, I don't know)
How do I begin to open a WIPO case?
http://www.wipo.int/amc/en/domains/
I'd suggest a lawyer letter first, maybe the owner will settle for less than a WIPO case. Don't offer to buy it from the owner, though, have the lawyer let them know that it is in violation of TM and WIPO.
BTW - I am not a lawyer and I do not play one on TV.