If the third party in question does not have the trademark rights they claim, or it is not a very strong claim. In most cases, the third party will need their trademark registered with the US Patent and Trademark Office (USPTO). The USPTO website has a trademark search engine that you can consult. This may also require a cybersquatting attorney to help determine if the trademark claim is strong enough.
When you are selling a domain name, you don’t want to suffer because of failed transactions or being tricked by defaulters. Safeguard your monetary dealings; the best way to do this is to take the help of a secure domain transfer and escrow service. The escrow system is highly beneficial because a buyer has to deposit money at the trusted source prior to purchase, and the dealing between a buyer and a seller takes place through a secure domain transfer and escrow service. This makes the transaction safer for both parties with the involvement of a neutral third party.
Listen to expert domainers on domainsherpa.com. Read anything by Michael Berkens, Frank Schilling, Eliot Silver, Morgan Linton, and Ron Jackson. Watch YouTube videos on domain investing. Read blogs like The Industry News Magazine at DNJournal.com. Search #domains on Twitter. Go to industry conferences. Understand the Google Keyword Planner tool inside and out.