Domain Names. How to avoid trademark infringement.

One pertinent question. Are all these domain names trademark free ? A new domain name not trademarked but coined with two trademarked names, can it be a case of infringement. There are scores of domains for sale which infringes when you take single names of these domain names and search for trademark registration.
Can a non trademarked website file a case of conflict of interest if your new domain name which maybe a variation but have the same business goals .